He had severe mental health issues since childhood that should rule people out from being legally allowed to own firearms. Reducing it to his being suicidal on the day in question is way too simplistic. Most people who are suicidal are not homicidal.
Your interpretation of the data is noted. And it is merely an interpretation of the data, is my point, for anybody left wondering. My interpretation is that if someone's blowing up barns and all the barns he's blowing up are brown, and nobody's blowing up any red barns, then probably the fact that they're brown means something. Your interpretation of the data is basically, "The fact that all the barns getting blown up are brown, and none of them are red, doesn't mean anything, it's just a coincidence."
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It's not. Suicidal people should be removed from guns. »
Any sort of violent criminal record
This can be gerrymandered, since liberal, Leftist cities and municipalities and states can redefine violent crime, such that violent crime doesn't count as violent crime, when it comes to trying to give violent criminals a second second chance.
along with certain mental health conditions.
Many mental health conditions, be honest. At least a dozen? Probably a lot more, if you list the disorders from the current DSM. Be honest.
Which gets back to my question again, how do you do that “ in a way that isn't easily abused, or arbitrary ”? you still haven't answered that. And if you don't answer that, your idea is dead on its feet; like saying, "Everything should be free!" which is impossible, and therefore vacuous.