I don’t think that something as extreme as mass hysteria could take place simply because no one wanted to think for themselves. Rather than people agreeing with a leader because they feel like it, I think people worry about an idea and “flock to follow” a leader because they don’t know what actions to take about the problem themselves. If someone offers a solution to a problem that they’re not sure how to fix, then they’re more likely to concede and follow that person. If someone didn’t care to think for themselves, then I don’t see why they would care to make any decision of that regard in the first place.
