Yes, we are in agreement that hate is a very bad thing.
The quick answer is: I don't know. But maybe you're not asking, "What *good*
does it do people to hate?" Maybe you're asking, "What *causes*
people to hate in the first place?"
I fondly believe that humans are born with love in their hearts (though it takes awhile for that to manifest; a newborn is by necessity strictly concerned with his/her own well-being). Hate is an artificial construct that has to be ingrained into people. Children are very trusting so if an adult teaches them to hate, they will probably take the lesson to heart. But it's easier and more natural to teach a child to love; that's what they're wired to do. Such is my fond belief (and optimism for the human species).
As for what *good*
it does to hate, that's an easy one. It does no good at all. Ever. Paint and clip and dress and modify your body all you want. Just don't hate it. And please, don't hate other people. Don't even hate your enemies. Just do what you can to go your own way, and let them go theirs.
Jesus is said to have said, "Do unto others as you would have them do unto you." Well, I would add to that, "Do unto yourself as you would have you do unto others." In other words, don't roll out the red carpet for everyone else and treat yourself like crap because you figure, "Hey, self-sacrifice is good thing, right?" I know some people think it is, but me, I think it's nasty business. Love all people, and treat all people fairly, and that includes yourself.
See? We're on the same page after all.