Do we
need Avon to not have committed this crime so much, we try to absolve him?
For me, killing Blake is one step too far (the same if Avon had killed Vila). Without extenuating circumstances, this is just more than I can take from him
Yet, many watchers feel that Blake's indirect replies and refusal to follow orders, combined with Tarrant's announcement that Blake had sold them out, were extenuating circumstances.
But, I think it's also more than he can take as a character. An Avon who has knowingly killed Blake has destroyed something essential about himself. Whatever Blake symbolized to him - hope, idealism, selflessness - and whatever part of him (however grudgingly) connected to that is dead.
This is closer to home for me. It isn't that we need Avon not to be guilty. (Mistakes happen) It's that Avon wouldn't accept the mistake. To continue the story, we tend to need Blake to survive, or the mistake to be less terrible. Although, I myself would like any PGP to start with Avon's mental state thereafter, and deal with the question of what it would take to get him to be, well, human again.