And you're intent on burying the problem in minutia to create the impression that it's impossible to solve it via regulation.
We can regulate firearm ownership and use similar to the way we regulate motor vehicle ownership and use. We license it, with strict requirements for obtaining specific various levels of licensing: for gun collectors, for long guns for hunting, pistols for home protection, pistols for conceal-carry, etc.,.. Those requirements including education, training, testing, vetting, and continued oversight. The intent being to deny firearms license to people who show themselves to be physically, mentally, emotionally, or otherwise incapable of fulfilling the responsibilities inherent to firearm ownership and use within our society. And, of course, for this kind of regulation to work, we would have to enforce it, rigorously. If you own guns now, and you want to legally keep them, you would have to get a license to do so, and register them all. Or you would have to get rid of them.