Interestingly, while Draco has done a lot of things in HBP that objectively deserve much cursing, it was his face-stomping Harry that made him so very unforgivable in many's eyes (probably because he neither cried over nor was punished, or looked like will *ever* be punished for it).
But of course I wasn't the only one who cheered at that scene, and not out of blind love for Draco or even more blind hate for Harry. I cheered because really, Harry had it coming a long time and in a way, he had deserved it.
When placing blame in a fight, this fandom bizarrely likes to focus on "who started it/asked for it". Sure, it wasn't very nice that the trio, and the twins and Lee from behind hexed Draco, Crabbe and Goyle into something akin to human experiments gone bad. Sure, it wasn't very nice that the Gryffindor gang then kicked their unconscious bodies out of the way, making sure they stepped on said bodies while they were at it. BUT, it was Draco & gang's fault to have been insulting Cedric's memory and giving the trio "death threats" in the first place, they were asking for it! And sure, it wasn't terribly nice either, that Harry and George together beat Draco into a bloody pulp, but again, he had insulted both their parents, and thus had *deserved* Harry, George (and Fred unsuccessfully) lashing out at him! And let's not get into the whole MWPP vs Snape thing, one ugly battlefield in terms of which side a fan stands behind.
So if one were to follow their logic, since verbal assaults are more than enough reason to warrant physical assaults, why was it that Harry infringing on Draco & co's privacy (remember, he hid under the invisibility cloak, he wasn't even just trailing them as a visible person) not asking for violent retribution? And this is *not* even what I meant by he had deserved violence from Draco, not exactly. It's that Draco is someone Harry has had 5 years worth of really bitter history with, from his perspective, Draco has 'started it' by being mean to Ron (while from Draco's perspective, Harry has started it by refusing his offer of friendship, and Ron has started it by hinting mockery of his name). And no matter who was to blame for starting their long-term feud, their interactions had been a long, looooooooooooong string of overreactions and disproportional "punishments" for each other's "crime".
Draco was damned from the beginning in Harry's mind when he unwittingly reminded Harry of his bully cousin Dudley, so whatever he said in Madam Malkin's afterwards were seen in a negative light even when Draco did not mean what he said then as an insult to Harry. Draco had to trash Ron, who Harry was already being friendly to, when Ron merely snorted at what he figured must be his name. From then on, things simply became worse and worse every year. And I don't believe either Harry or Draco had been holding this moral ruler in their mind measuring what their rival objectively deserved for offending them, instead they had always been, simply acting on their emotions. Remember we are talking about a boy who at 12 said he wished a girl who had done him no severe wrong dead, and another boy who at *16* crossed fingers that his most hated professor (who had saved his life before!) would die sometime this year. I never considered any of their nasty behaviors against each other 'justified', I find them simply 'understandable'. But it greatly puzzles and annoys me, when people take the trio, twins and Lee's consquence-less actions at the end of GOF as meaning that the six of them had done 'no wrong'- same with when people say Harry was right or at least 'not that wrong' in using violence against Draco, the whole incident was just about Umbridge being a total bitch giving Harry a punishment he did not deserve at all.
So when I said Harry sort of deserved the face-stomping, I meant it in the sense that it was 'his turn' to be on the receiving end for punishments disproportional to his 'crime', because I have never, and still do not believe what was between Harry and Draco in the past five years had anything to do with justice, or morals.
Though things are certainly different from HBP onwards. With both boys having leveled themselves out of schoolboy rivalry, their confrontations in the very last book of this series would most certainly, finally be about right and wrong.