Right again, Zukiphile.
However, the problem with this whole line of discussion is the underlying assumption that everyone who "goes postal" (to use a somewhat antiquated term) is a priori
mentally ill, and that all we need to do is identify "those people" and render them harmless. Not so. Rage at injustice, whether real or perceived, is a natural, human thing, and a useful one. Violence as an outlet for that rage is also human. We all, like it or not, have the capacity for both. We all have the capacity to do evil by choosing to direct that rage and violence at the innocent.
It's human (and a behavior seen in other animals, as well) to use those who are relatively defenseless as targets for that rage and violence. We all know the famous old example: man gets yelled at by his boss... comes home and yells at his wife... who yells at the kid... who kicks the dog. (My dog sometimes claws at and humps her blankie after I tell her not to do something.
None of this adds up to mental illness, just to being human. This means that we can't, in fact, always predict who's going to "snap" and commit mayhem.
By scapegoating the mentally ill, are we sure we're not engaging in another form of this behavior? Better we should use the energy from whatever rage we have, either at the people who do kill innocents, or at those who would deny us our rights, more constructively; for example, we could look at the objective social conditions that lead to that level of rage in the first place: social isolation, bullying, and the powerlessness felt by those who lose jobs and homes to economic conditions over which they have no influence whatever... just to name a few. (And, yes, it may well be that some mentally ill people are more likely to react violently to these things -- but they are
often reacting to something in their lives.)