I don't think Xander can technically be described as a murderer, but I do find it disturbing that he appeared to show no remorse for his actions and that the rest of the Scoobies - including Giles, never took him to task for it at all.
It's also very disturbing to think about the way he pretended not to know what was going on during the episode - his conversation with Giles in the street immediately after his and Anya's song for instance. He must have known then that it was his doing, as, when he owns up at the end, he says that he knew there would be songs and dancing. The lies seemed to come too easily and I found this quite creepy.
Something else to think about is that Xanders actions were selfishly motivated - he did it to make sure he and Anya 'turned out alright'. He was the cause of at least one death, and mortal danger for people he professes to care for deeply just to get what he wanted.
It's not the first time either - in Season 2 - Bewitched, Bothered & Bewildered, he gets Amy to help him with a spell in order to get back at Cordelia which puts all of his friends in danger - similar scenario.
Whilst he's not a murderer, his actions in both these cases are definitely more than a case of 'accident' or 'carelessness'. I would say that someone who spends that much time around the forces of darkness has absolutely no excuse not to understand the relationship between actions and consequences.
The worst thing about it for me was that he watched Buffy beginning to burn and STILL didn't say anything - was he prepared to let his friend die knowing that he had information which, for all he knew, may have helped them stop it?
Given Xanders behaviour towards Spike all through Seasons 5 & 6 and especially after Seeing Red, I think it's a great piece of irony that it was Spike who stopped Buffy from combusting.
It could possibly be argued that Spike saved Buffy from Xander.
::evil:: LOL ::evil::
Xander has always been a favourite of mine but in Season 6 he seemed to be becoming more and more like the jerks who used to pick on him in highschool - a classic case of the abused becoming an abuser perhaps.
I hope they bring back funny, generous, big-hearted Xander for S7, cos I miss him. *whine*