There are a number of reasons. One is they are obsessed with the idea of power over other people. They are not in charge, and they want to tell others what they must do.
Another is they are not happy, and they hate the idea of anyone else being happy when they are not. (Misery loves company)
Three: They demand perfection.
Life is not perfect.
Reality is not perfect.
So, they are willing to destroy everything (the good) in a futile attempt to create perfection.