Are there kingdoms of emotion where logic is taboo, dare not show its face, zones where reason is too intimidated to speak?

Moral philosophers make full use of the technique of thought experiment. In a hospital there are four dying men. Each could be saved by a transplant of a different organ, but no donors are available. In the hospital waiting room is a healthy man who, if we killed him, could provide the requisite organ to each dying patient, thereby saving four lives for the price of one. Is it morally right to kill the healthy man and harvest his organs?

Everyone says no, but the moral philosopher wants to discuss the question further. Why is it wrong? Is it because of Kant's Principle: "Act in such a way that you treat humanity, whether in your own person or in the person of any other, never merely as a means to an end, but always at the same time as an end." How do we justify Kant's principle? Are there ever exceptions? Could we imagine a hypothetical scenario in which…

What if the dying men were Beethoven, Shakespeare, Einstein and Martin Luther King? Would it be then right to sacrifice a man who is homeless and friendless, dragged in from a ditch? And so on.

Two miners are trapped underground by an explosion. They could be saved, but it would cost a million dollars. That million could be spent on saving the lives of thousands of starving people. Could it ever be morally right to abandon the miners to their fate and spend the money on saving the thousands? Most of us would say no. Would you? Or do you think it is wrong even to raise such questions?

These dilemmas are uncomfortable. It is the business of moral philosophers to face up to the discomfort and teach their students to do the same. A friend, a professor of moral philosophy, told me he received hate-mail when he raised the hypothetical case of the miners. He also told me there are certain thought experiments that divide his students down the middle. Some students are capable of temporarily accepting a noxious hypothetical, to explore where it might lead. Others are so blinded by emotion that they cannot even contemplate the hypothetical. They simply stop up their ears and refuse to join the discussion.

"We all agree it isn't true that some human races are genetically superior to others in intelligence. But let's for a moment suspend disbelief and consider the consequences if it were true. Would it ever be right to discriminate in job hiring? Etcetera." My friend sometimes poses this very question, and he tells me that about half the students are willing to entertain the hypothetical counterfactual and rationally discuss the consequences. The other half respond emotionally to the hypothetical, are too revolted to proceed and simply opt out of the conversation.

Could eugenics ever be justified? Could torture? A clock triggering a gigantic nuclear weapon hidden in a suitcase is ticking. A spy has been captured who knows where it is and how to disable it, but he refuses to speak. Is it morally right to torture him, or even his innocent children, to make him reveal the secret? What if the weapon were a doomsday machine that would blow up the whole world?

There are those whose love of reason allows them to enter such disagreeable hypothetical worlds and see where the discussion might lead. And there are those whose emotions prevent them from going anywhere near the conversation. Some of these will vilify and hurl vicious insults at anybody who is prepared to discuss such matters. Some will pursue active witch-hunts against moral philosophers for daring to consider obnoxious hypothetical thought experiments.

"A woman has an absolute right to do what she wants with her own body and that includes any foetus that it might contain. I don't care if the foetus is fully conscious and writing poetry in the womb, the woman still has the right to abort it because it is her body and her choice." Do we discuss the hypothetical intra-uterine poet, or does emotion simply close down the discussion, in either direction? Do we think the woman's right is absolute, absolute, absolute – end of? Or do we think abortion is wrong, wrong, wrong; abortion is murder, no further discussion.?

"We agree that cannibalism is wrong. But if we don't need to kill someone in order to eat them, can we discuss why it would be wrong? Why don't we eat human road-kills? Yes, it would be horrible for the friends and relatives of the dead person, but suppose we hypothetically know that this person has no friends or relatives of any kind, why wouldn't we eat him? Or is there a slippery slope that we should consider?" Do we proceed to discuss such questions rationally and logically with the professor of moral philosophy? Or do we throw an emotional fit and run screaming from the room?

I believe that, as non-religious rationalists, we should be prepared to discuss such questions using logic and reason. We shouldn't compel people to enter into painful hypothetical discussions, but nor should we conduct witch-hunts against people who are prepared to do so. I fear that some of us may be erecting taboo zones, where emotion is king and where reason is not admitted; where reason, in some cases, is actively intimidated and dare not show its face. And I regret this. We get enough of that from the religious faithful. Wouldn't it be a pity if we became seduced by a different sort of sacred, the sacred of the emotional taboo zone?

Moving from the hypothetical to the real, if you raise the question of female genital mutilation, you can guarantee that about half the responses you get will be of the form "What about male circumcision?" and this often seems calculated to derail the campaign against FGM and take the steam out of it. If you try and say "Yes yes, male infant circumcision may be bad but FGM is worse", you will be stopped in your tracks. Both are violations of a defenceless child, you cannot discuss whether one is worse than the other. How dare you even think about ranking them?

When a show-business personality is convicted of pedophilia, is it right that you actually need courage to say something like this: "Did he penetratively rape children or did he just touch them with his hands? The latter is bad but I think the former is worse"? How dare you rank different kinds of pedophilia? They are all equally bad, equally terrible. What are you, some kind of closet pedophile yourself?

I have met the following reaction when discussing the vexed and terrible question of Israel/Palestine. Israeli friends have said to me things like, "We needed a Jewish state because, after the Holocaust, we realised that nobody else was going to look after us, we'd have to look after ourselves. Jews have been downtrodden for too long. From now on, we Jews are going to stand tall and take care of ourselves." To which, on one occasion, I replied, "Yes, of course I sympathise with that, but can you explain why Palestinian Arabs should be the ones to pay for Hitler's crimes? Why Palestine? You surely aren't going to stoop to some kind of biblical justification for picking on that land rather than, say, Bavaria or Madagascar?" My friend earnestly said, "Richard, I think we had better just terminate this conversation." I had blundered into another taboo zone, a sacred emotional sanctuary where discussion is forbidden. The emotions aroused by the Holocaust are so painful that we are not allowed even to discuss such questions. A friend will terminate the conversation rather than allow entry to the sanctuary of hurt emotion.

On Twitter during the current horrible events in Gaza, I wrote the following:

I was immediately bitterly attacked by friends of Israel. But then I quoted Sam Harris to the effect that "Hamas publicly says they'd like to kill every Jew in the world" and I went on to raise Sam's hypothetical question: What does that say about Hamas's probable actions if positions were reversed and they had Israel's military strength? Sam's suggestion that this contrast might actually be demonstrating restraint on Israel's part, unleashed a storm of furious accusations that he, and I, relished the bombing of Gaza's children.

I also quoted Sam as saying "I don't think Israel should exist as a Jewish state." So of course I, and Sam, got vituperative brickbats from Israel and from American Jewish interests. I summed up my position on the fence (linking to an interview with Christopher Hitchens) as follows: "It is reasonable to deplore both the original founding of the Jewish State of Israel & aspirations now to destroy it." But I swiftly learned that emotion can be so powerful that reasonable discussion – looking at both sides of the question dispassionately – becomes impossible.

Apparently I didn't learn swiftly enough – and I now turn to the other Twitter controversy in which I have been involved this week.

'"Being raped by a stranger is bad. Being raped by a formerly trusted friend is worse." If you think that hypothetical quotation is an endorsement of rape by strangers, go away and learn how to think'

That was one way I put the hypothetical. It seemed to me entirely reasonable that the loss of trust, the disillusionment that a woman might feel if raped by a man whom she had thought to be a friend, might be even more horrible than violation by a stranger. I had previously put the opposite hypothetical, but drew an equivalent logical conclusion:

These two opposite hypothetical statements were both versions of the general case, which I also tweeted:

The point was a purely logical one: to judge something bad and something else very bad is not an endorsement of the lesser of two evils. Both are bad. I wasn't making a point about which of the two was worse. I was merely asserting that to express an opinion one way or the other is not tantamount to approving the lesser evil.

Some people angrily failed to understand that it was a point of logic using a hypothetical quotation about rape. They thought it was an active judgment about which kind of rape was worse than which. Other people got the point of logic but attacked me, equally furiously, for choosing the emotionally loaded example of rape to illustrate it. To quote one blogger, prominent in the atheist movement, 'What would have been wrong with, "Slapping someone's face is bad, breaking their nose is worse"? Why need to use rape?'

Yes, I could have used the broken nose example. I accept that I must explain why I chose to use the particular example of rape. I was emphatically not trying to hurt rape victims or trivialise their awful experience. They get enough of that already from the "She was wearing a short skirt, I bet she was really begging for it Hur Hur Hur" brigade. So why did I choose rape as my unpleasant hypothetical (in both directions) rather than the "breaking someone's nose" example? Here's why.

I hope I have said enough above to justify my belief that rationalists like us should be free to follow moral philosophic questions without emotion swooping in to cut off all discussion, however hypothetical. I've listed cannibalism, trapped miners, transplant donors, aborted poets, circumcision, Israel and Palestine, all examples of no-go zones, taboo areas where reason may fear to tread because emotion is king. Broken noses are not in that taboo zone. Rape is. So is pedophilia. They should not be, in my opinion. Nor should anything else.

I didn't know quite how deeply those two sensitive issues had infiltrated the taboo zone. I know now, with a vengeance. I really do care passionately about reason and logic. I think dispassionate logic and reason should not be banned from entering into discussion of cannibalism or trapped miners. And I was distressed to see that rape and pedophilia were also becoming taboo zones; no-go areas, off limits to reason and logic.

"Rape is rape is rape." You cannot discuss whether one kind of rape (say by a 'friend") is worse than another kind of rape (say by a stranger). Rape is rape and you are not allowed even to contemplate the question of whether some rape is bad but other rape is worse. I don't want to listen to this horrible discussion. The very idea of classifying some rapes as worse than others, whether it's date rape or stranger rape, is unconscionable, unbearable, intolerable, beyond the pale, taboo. There is no allowable distinction between one kind of rape and another.

If that were really right, judges shouldn't be allowed to impose harsher sentences for some rapes than for others. Do we really want our courts to impose a single mandatory sentence – a life sentence, perhaps – for all rapes regardless? To all rapes, from getting a woman drunk and taking advantage at one end of the spectrum, to holding a knife to her throat in a dark alley at the other? Do we really want our judges to ignore such distinctions when they pass sentence? I don't, and I don't think any reasonable person would if they thought it through. And yet that would seem to be the message of the agonisingly passionate tweets that I have been reading. The message seems to be, no, there is no spectrum, you are wicked, evil, a monster, to even ask whether there might be a spectrum.

I don't think rationalists and sceptics should have taboo zones into which our reason, our logic, must not trespass. Hypothetical cannibalism of human road kills should be up for discussion (and rejection in my opinion – but let's discuss it). Same for eugenics. Same for circumcision and FGM. And the question of whether there is a spectrum of rapes, from bad to worse to very very much worse, should also be up for discussion, no less than the spectrum from a slap in the face to a broken nose.

There would have been no point in my using the broken nose example to illustrate my logic, because nobody would ever accuse us of endorsing face-slapping when we say, "Broken nose is worse than slap in face". The point is trivially obvious, as it is with the symbolic case of "X is worse than Y". But I knew that not everybody would think it obvious in the special cases of rape and pedophilia, and that was precisely why I raised them for discussion. I didn't care whether we chose to say date rape was worse than dark alley stranger rape, or vice versa. Nor was I unaware that it is a sensitive issue, as is pedophilia. I deliberately wanted to challenge the taboo against rational discussion of sensitive issues.

That, then, is why I chose rape and pedophilia for my hypothetical examples. I think rationalists should be free to discuss spectrums of nastiness, even if only to reject them. I had noticed indications that rape and pedophilia had moved out of the discussion zone into a no-go taboo area. I wanted to challenge the taboo, just as I want to challenge all taboos against free discussion.

Nothing should be off limits to discussion. No, let me amend that. If you think some things should be off limits, let's sit down together and discuss that proposition itself. Let's not just insult each other and cut off all discussion because we rationalists have somehow wandered into a land where emotion is king.

It is utterly deplorable that there are people, including in our atheist community, who suffer rape threats because of things they have said. And it is also deplorable that there are many people in the same atheist community who are literally afraid to think and speak freely, afraid to raise even hypothetical questions such as those I have mentioned in this article. They are afraid – and I promise you I am not exaggerating – of witch-hunts: hunts for latter day blasphemers by latter day Inquisitions and latter day incarnations of Orwell's Thought Police.

This blog first appeared on Richard Dawkins' personal blog, and can be read here