Americans were more concerned about almost everything: legal liability, data privacy, interactions with non-self-driving vehicles, system performance in poor weather, and the self-driving cars, in general, being worse than humans. 

It's only fitting for the United States to have this two-faced reaction to new technologies. We are the country, after all, that spawned the semiconductor and computing industries right alongside the modern environmental movement in the 1960s and 1970s.

Across countries, people who had more automatic technologies installed on their current vehicles—such as advanced speed control—were both more interested in self-driving car technology and more worried about the downsides. 

Proximity to new technologies doesn't necessarily breed contempt, but rather familiarity, a realistic sense of what new technologies can and cannot do for us. The closer we are to technologies, the less likely we are to see them in purely optimistic terms. 

That was also the conclusion our Adrienne LaFrance came to in examining a Pew survey about Americans' views on the next 50 years of technological development. "The survey revealed that people are mostly optimistic about how tech will change our lives in the long run," she found. "But they're apprehensive about specific technologies that are closer to reality."

If ever there was a time when people were unreservedly excited about new technology, it is over. But the excitement remains, it's just complicated by the trajectory of the 20th century. No matter how much mechanical or computational power a country possesses, utopia keeps retreating into the future.