That is not to say, of course, that one should feel positively toward everyone and everything. It is right to despise certain things, even to the point of working toward their utter destruction. It is important, however, to maintain a perspective that one is destroying such things because it is necessary, rather than because it is fun.
When you engage in self-pity, nobody is going to feel sorry for you but yourself. Self-pity is poor box office. Your self-pity will drive your successful friends away from you and you will be surrounded by losers like yourself.
Liberalism, of course, teaches that victimhood is a good and noble. A woman who submits to rape is more noble in her acceptance of the pain than one who shoots the rapist--making him suffer because of her unwillingness to do so. In their eyes, a team that loses massively on an unfair playing field can claim they're good enough that they should have won, far more effectively than can a team which lost narrowly on a fair one. Thus, magnifying the unfairness against them is more important than trying to win.
I can honestly say that I hate nobody. I might despise things that other people do - like murder, drugs or advocate for higher taxes. But I do not hate them personally and do not waste a minute of my life hating them.