Some people are just looking for an excuse to kill. Anybody.
That's why they buy mil-spec weaponry.
Going after blacks or Muslims is still considered bad form, even by most Conservatives. And killing Jews is SO Twentieth Century, especially since they play such a vital role in most evangelical apocalyptic fantasies. But protecting the nation from a Communist tyranny, an atheist takeover or a statist conspiracy still manages to carry some sort of patriotic cachet.
It makes them feel better about shooting total strangers. As Mr Bowman says, “If I have to be a patriot, I will,” I bet he can't wait.