> How does the moral calculous work for Americans? Genuinely curious. Is it “something bad is being done to me, I am therefore justified to use any means necessary” kind of thing, or there is something else/more?

Generally speaking, it works just like it works everywhere else--we don't execute people on the street. We sometimes have the legal grounds to use lethal force in defense of our safety or that of our property (rarely, but apparently in Texas), and we very rarely choose to actually use it.

Intrinsic morals don't have a whole lot to do with laws.