What sort of mental illness are we talking about?

Do they think that the queen is a lizard and the government is putting chemicals in contrails? I really don't care if they have a gun. Lizard and chemtrail people are clearly loony, but they seem perfectly harmless.

Instead are they a psychopath fascinated with violence? In that case yeah, I am not comfortable with them having a gun... but if we know who they are then why the hell are they not institutionalized already, rendering the issue moot?

The whole point of the article was to question the validity of the diagnosis of mental illness, which you completely ignore when you blithely add the disclaimer that "these folks" refers only to people who are mentally ill.