I'm sure this sounds like a big nothingburger from the perspective of, you know, people he isn't threatening.
How can you excuse that behaviour? How can you think someone like that can be trusted with any weapons? How naive and morally bankrupt do you have to be to build a gun for that kind of person, and think that it won't be used irresponsibly?
That it won't is a mixture of cowardice, cynical opportunism, and complicity with unprovoked aggression.
In which case, I posit that yes, if you're fine with threatening or inflicting violence on innocent people, you don't have a moral right to 'self-defense'. It makes you a predator, and arming a predator is a mistake.
You lose any moral ground you have when you are an unprovoked aggressor.