No I'm not saying every shooter is a Libertarian, let alone that every Libertarian is a potential shooter. That's nuts.

But US culture is far more libertarian than any other with which I am familiar. The drive to be a "rugged individual", disconnected from larger society. It's not just the "fuck you I've got mine" zero tax greed. That's a symptom, but can also come from other mindsets. But add that to the idea of being a "self-made man" (as if you don't use public roads, public services, public regulatory authority no matter how self-employed you may be, how many acres you own or how much food you grow yourself. Who educated your customers? Who oversees the currency they give you?), the idea of not being one of "them" (there's a reason the vast majority of mass shooters are male and white), the idea of bring able to "take care of yourself" (against TEOTWAWKI fantasies no less. Mad Max is fiction...) and it becomes the rejection of human civilized history with its continued and constant push towards group and collective progress.

When you talk yourself into thinking you are one of the few real men carrying all the spongers, it's a pretty short step to not caring if they live or die, and another tiptoe into wanting the latter.

Sure other countries have terrible classism, many have virulent tribalism that dehumanizes the other. But no 20th-generation British nobleman thinks he did it all by himself (quite the opposite, his snobbery comes from those generations) and no Hutu considers himself a self-made master of men (again, his drive is to help his tribe and be against Tutsis for that reason).

Look at how young people in Asian cultures suffer under collective mindsets. With no individualism, their societies fell far behind the west technologically, artistically and culturally. Risk-taking behaviors are stigmatized, which results in societal stagnation.

Our individualism has led to the creation of entire industries that people thought absurd at the time, but which turned out to be revolutionary.

Of the two though I think authoritarianism has a far worse track record of horror and death.