annoyed with Xander for walking out on his wedding. It's one of my least favourite parts of Buffy and I don't actually think that it was in character for Xander. I think he's far likely to go ahead, with doubts, then have it fall apart later than just walk out like that - one of the reasons Season 6 is my least favourite.
I don't think Giles murdering Ben is a particularly bad example. Buffy slays Demons all over the place in every episode. I know Ben was an innocent, and it was a difficult situation, but it doesn't reflect badly on Giles.
"Helpless" does reflect badly on him, but it reflects badly mostly on the whole organisation of Watchers - who are portrayed as useless and corrupt. At least he feels guilt over it, and gets dismissed from his post because of it.
I never said that Giles hasn't made mistakes, but he hasn't done anything selfish or evil in the course of the show - lapses in judgement are a different matter.