You hated it because it had a mean character in it? Your prerogative, I suppose. I thought it was a fantastic movie, despite not liking every person in it.
I hated it because its message was perverted. The "mean" character was rewarded -- not punished -- for his most sadistic act (the last 10 minutes of the movie), and as sofal has pointed out here, audiences seemed to have taken his behavior as the norm when pushing students to greatness. If the movie had ever implied that greatness can be achieved without abuse (which it can), I'd have had no problem with it.
