Any danger to society should be removed from it, in a way that attempts to stop the killing urge where possible. Really, predisposition, mental illness, war-vet snapping; I don't care. If my sister can't walk safely to school because of a person, that person should not be on the streets. It really is as simple as that.
And about predisposition: I have several papers on me being predisposed for agressive behaviour, and I was aware of this before the health system. What did I do? I DEALT WITH IT. When I'm angry, I write something, chop off a few heads on Morrowind, go fishing, or anything else that comes to mind that can help me get rid of the anger surge. Any predisposed person who does not cope with it should be removed.
By the way, I should perhaps clarify one thing: I use the word remove a lot, but I mean in the "not longer out in society"-way, not the "kill with legal fire"-way. =P