I’m torn on the idea of arming leftists in the current climate. I don’t disagree with you there. I live in a somewhat rural area that is heavy Trump and the right wingers are heavily armed. I don’t blame a trans person for arming themselves to defend themselves in an area like this, and my post history reflects as much.
That said there is a difference between arming yourself and actively contributing to increasing the amount of arms in the world. And what made it interesting is you claimed this is an ethical and moral issue. If your friend worked to only arm leftists that would be an interesting take. I doubt this is the case though. I am assuming they are like any capitalist based on your first line - anyone’s money is good enough.
To answer your question as others have said the hammer has a utilitarian purpose, as do knives, as does dynamite. With the exception of something like skeet shooting guns sole purpose is to rob the consciousness of a living being. I do not believe that the sport outweighs the risk. There are far less dangerous ways to hunt, we’ve banned things like lawn darts for less when the danger outweighs the utility. America just has a raging hard on for guns because of military fetishism
I think whether mass shooters are mentally ill is debatable on a case by case basis, some obviously yes, some less obviously.
But what I’m saying is this point is moot because even if 100% of mass shooters are “mentally ill” and that is the driving force behind their culpability the individuals saying “we need better mental health care in this country” in the wake of gun violence are so full of shit and obviously using the topic for misdirection with no intention for meaningful change. This is clearly evidenced by the fact that mental health services have been systematically defunded year after year for decades, very often by the same individuals who clamor the same.