i think this is due to two human traits/biases, 1) seeing something wildly out of the norm leads to doubts about one's perceptual abilities immediately after the fact (in other words, did I just see that happen, I know I saw it, but that can't have been what just happened...) and unless you write down careful notes immediately you will doubt that it actually happened. 2) people want to be right because it makes them feel safer that the world they know is the world they live in, hence people will hold out hope that all the weirdness can be explained away (and sometimes it can).

Most people aren't psychopaths. The man was crazy, but he was still a person and didn't deserve to die.

You should celebrate the fact that even people who he antagonized were upset by his death. Even if they reacted irrationally, at least they reacted at all.

There’s a big difference between empathy and guilt. That people feel guilty and responsible for what happened to the man is a legacy of his manipulation, and not something to be celebrated.