On what grounds? Locking people up who have not committed any crime is BS. You want to give the government power to determine who is a "lunatic" and just start locking people who are "crazy" away? The potential for abuse there is huge. Ie. "Oh look, that spat guy over there supports gun rights and lives off the power grid. That guy is clearly crazy, lets lock him up, never know what he is going to do next." That's way too much power for the govt. to have.If you identify such a lunatic, you need to lock them up.
Leaving them free to roam while making it slightly more difficult to get a gun is insanity