Well, in Canada, there are provincial firearm officers (Chief Firearms Officers) who will determine who can or can't own a gun. This is done of course by checking an individual's criminal records and it is based on past behaviour. Also, in order to get a gun licence (Possession/Acquisition Licence) Canadians must pass written and practical examinations to demonstrate that they have a comprehensive understanding of firearms themselves as well as the applicable storage, transport and usage laws. (There is even a separate set of exams for those wanting a hunting licence).
If married or common law, the applicant must have the approval of the spouse in order to obtain the gun permit. As a matter of fact, even an ex-spouse or boy/girlfriend (within a certain number of years) can veto a firearms acquisition. (That's always been a favourite rule of many gun owners).
So there are a complete series of checks, double checks (as in the case of a "restricted" firearms acquisition) and examinations to determine an individuals responsibility with respect to firearms ownership.
Admittedly, there is no guarantee that someone might not "snap" and break the law, however I am not aware of any laws made based on what an individual might do (without a prior history to indicate likelihood). If that were the case, then no-one should possess a driver's licence because there might be the possibility that the individual could drive impaired, cause an accident or even kill somebody. Would you want laws based on this rationale???