lol, Gambit went to join Apocalypse team; he personally chose to become a Horseman. Angel lost his wings to the events of Mutant Massacre and was completely suicidal because of that. Apocalypse offered Warren a way to stop his pain and for his wings to come back.
Batman didn't betray the Justice League. He, as a hero, did what he was supposed to do. Protect the innocent from the bad guys (even the bad guys who were once good).
Adam Beechen hit it right on the nail. It's all about the intentions.
Did the hero in question betray his team mates because of personal reasons?
Was the hero forced to betray his team?
Was the hero aware that he was betraying his team?
Does the hero have a history of betrayal?
Is the hero sorry for his betrayal or just sorry he was caught?
I think those are the questions to be considered when deciding if a hero is to be forgiven by those who he betrayed.