But let's think about this for a second. You are saying these people shouldn't be barred because they haven't been found to be a danger to themselves or others? Obviously. You can't restrict a right based upon nothing. This isn't Iran. But if probable cause is found, then you should restrict the right.
I guess what I am getting at is I don't really understand your position. Are you against guns because some people slip through the system? Because if that is the case, well that isn't right. People rarely slip through the system, but more importantly the act of any form of ban is not really the answer to people who are dangerous to themselves or others. The answer is awareness and educating the public.