"Criminals and those who are not mentally stable, and those with restraining orders are prohibited from possessing firearms. ANY other citizen over the age of 18 can get guns, as they wish."

"UNTIL the person is recognized by a court or medical evalution as mentally impaired or deficient, they are presumed sane- right????"

What about a person who has been treated for mental problems and then released? Isn't that person legally sane?
Can you honestly say that you have never known a person who has never been clinically diagnosed as "unstable", but to whom you would be uncomfortable selling or loaning a gun because of what you know about them? Would the problem that you know about be obvious to a gun dealer who met him briefly?