I imagine one of the reasons people cling to their hates so stubbornly is because they sense, once hate is gone, they will be forced to deal with pain.
I would go further and say that hate is one of the simplest, most effective, and most universal ways of getting control of our emotional lives.
A trivial example is the way older adolescents turn their worries about whether they are cool and with-it into hatred of bands and TV shows popular with 12-year-olds. At the most serious level, Nazis and Bolsheviks turn all the pain and dislocation of modernity into genocide.
I believe that hate is the worst thing we are capable of, and I believe nothing more strongly than this. The most radical idea ever expressed, maybe the most radical possible idea, is that we should love our enemies. Keeping this in mind, always, is the best cure for the political animosity that is our besetting sin.
Some people think this is a path to a sort of quiet irrelevance, meditating on a mountain while the bastards take over the planet. But you do not have to hate people to oppose them. You do not have to give into venom to work for change. There are better responses to the pain of the world than hate.