It is clear to me that if a person sees nothing wrong with allowing a mentally ill person with a violent history to buy a gun with no waiting period or background check, then it is obvious that self eveident common sense is absent with regard to that person. I therefore resign, and move to the real world, and converse with those that understand that insanity and semi-automatic weapons don't mix.
Who decides who is mentally ill or not? The government? They can already declare you a terrorist with no evidence and lock you up forever without a trial or lawyer. In fact, although it cannot be proven, they probably just kill them ... how would you know if they don't?
Keep in mind, that in order to to bar mentally ill people from buying a gun, there must be a NATIONAL REGISTRY of mentally ill people. Such a registry could be used to force mentally ill people to be sterilized. Later it could be used to force mentally ill people to be "euthanized." Also, since the government can decide who is mentally ill, and who is not, without evidence, it is most likely they would use this against anyone who could or has resisted them.
Do this sound like crazy talk, then read this thread: