bespangeled
Scooby
Not giving him a pass, like I said, I don't condone his actions at all.
But as far as having a dark side goes: Giles and his gang seemed pretty well aware that what they were doing was dark and destructive; that's what they were into.
Xander genuinely seemed to think he was summoning a happy, non killing, music demon... he was a massive dumbass and I personally think he should have been chastised for it a hell of a lot more than he actually was, but I don't think it was indicating that Xander had darkness deep within him.
Xander gets a pass because he isn't seen as anything but an idiot. I can't give him one because he knew better in each case and still did what was easiest. Even with leaving Anya at the altar - he had doubts and never expressed them, he literally refused to face Anya and left her alone to deal with the aftermath, and then he complained about how miserable he was. His darkness was more in the reckless endangerment because he took chances knowing possible consequences and never took responsibility for his choices.