People must be allowed to express their emotions, even nasty ones like hatred. It does no good, and often does great harm, to prohibit the honest expression of any kind of emotion. (I'm not sure that sociopathy even counts as an emotion, so prohibiting cries of "Fire!" in a crowded theater can reasonably be prohibited.)
When you suppress expression of emotion, it can go into several places. It can just fester inside the person who's trying hard not to express it, until one day it explodes. Or the person can quietly find others who agree with him and form a clandestine group that never has to undergo public review so they can get pretty crazy.
As someone famous once said, "Sunlight is the best disinfectant."