For those who say you can choose to be drunk but NOT choose to be crazy....
I rest my case.
On a more serious note, I don't think he was crazy, I think he snapped and then went crazy. He was fine until his wife called him and told him something that set him off. He flew home and lost it, killing her in the process. Once the reality set in of what he did he went off the deep end. Fear of his son growing up with what he did besides the fact of his handicap which had to play a factor into Benoits feelings towards his son, he contemplated it for a day and decided to end his son's life.
Not being able to live with what he had done along with going to jail and all the other ramifications (Friends/family/WWE/judicial system) that he would have to face, he took his own life, which after he killed his whole family took a day in itself to come to that conclusion.
I don't think he was crazy, I think he lost his temper in a fit of rage (Like it has been documented in the past with his abuse and furniture smashing)(BENOIT SMASH!
) and killed his wife, which was the point of no return. And return he didn't.
Note: I think it's eerily fitting that his signature taunt was the thumb across to throat as in he's going to cut off your head or it can now be taken as the media has thrown around so much lately, "asphyxiation".