Yes you should write it. It may be controversial, but it is something I can see happening - there have been times myself when i have thought about wanting to just shoot the lot of them (although even if I did have a gun I am at least 99% sure I would never have done it). If you can present it so that the reader really empathises with the character and gets to the stage that they can understand why he does what he does at the end, then I think it could be really good. I always think that people do what they do for a reason, even in these extreme cases, and that if you were that person you would realise that they didnt have much of a way out. I think to get the the stage of shooting people though you would have to have a disociation from reality, something I have had when i have been very depressed, which stops him from acting morally.
It is true that it isnt a very positive message to give about AS, but perhaps it is something that could happen (and maybe has already, I dont know the details of the people that have done such a thing).
p.s. I didnt yet read your segment of the story. I will do so now.