I don't know why everybody hates Sasuke either. Sure, the kid has some flaws, but then.. who doesn't?

Yeah, it was bad that he went over to Oros side, but look at it from his POV. He got his ass kicked by his brother. Everybody seems to be getting ahead of him. His brother added insult to injury. Come on, people. He was scared, confused and angry.

Now, his weakness however is : He has the power of the Uchiha Sharingan, and is obviously the most gifted, as far as raw talent is concerned. But.. he doesn't make full use of it, and instead of trying to better himself, he is constantly comparing himself to others. Then, when he sees that he isn't the shit, he runs away and starts to feel insecure about himself.

And where people got the idea of him being selfish is beyond me. He showed brave acts of heroism and friendship, when he took all those blows from Haku back in the wave arc. He also obviously cares for his team-mates, enough to not let them know about his cursed seal. And, he shows grief, when he leaves w/the sound.