Maybe it's because a sizeable portion of the population is also fact-free, incapable of understanding measurable reality, and vulgarly hateful somewhere in their mean little hearts where they absolutely believe they are right about everything and that someone else is responsible for all their problems. It's beyond disturbing.   

I think Stanley Milgram shed a lot of light on the subject with his experiment in the 60s, but it doesn't explain everything.  A large portion of humans are eternally capable of committing horrible acts for supposedly "good" reasons. Trump and the increasing disparity between the rich and everyone else have provided a lot "good" reasons for a lot of people to illustrate just how dangerous humans are to themselves and everything else.  We need that benevolent despot that Mark Twain wrote about a while back, but I don't think we're going to get one.