Your question is missing some words, but I'll assume you mean the people with mental instability. Here in the US, people that have been involuntarily put in for mental treatment are (supposed) to be put on the no-buy list. The recent kerfluffle about "mentally handicapped people being allowed access to guns" was the denial of US veterans (reporting through the VA admin) of owning firearms if they needed assistance balancing their checkbooks, for one example. Supposedly, as rumor goes, Einstein had trouble keeping his checkbook balanced. I don't recall anyone crying for denial of his rights.
The reporting to NICS/FBI is spotty, at best (see recent church shooting in TX), and getting past HIPPA laws for mental reporting is a fight, also. The laws are there, but bureaucrats have to get their game together, too. No law is going to stop a determined attacker, they will just go black market (see gun/explosive attacks in Europe), or find another "vehicle". (See what I did there?) No one is 100% safe, anywhere, and no law ever prevented a crime. Laws only spell out what IS illegal, and proscribe a punishment for those who choose to ignore it. Murder has been illegal for millennia, but it still occurs.
Your turn!!! 
ETA: Welcome to DU!
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