I think you're getting wrapped up in the word choice here. Someone espousing these beliefs is supporting the killing of cops and soldiers, an act which is very often reprehensible in the same circles.
They tend to believe the threat is enough and that they'd never have to act on their threat (rendering it meaningless), or that all of the cops/soldiers will just let them kill the politicians (and killing a politician for a differing political belief is somehow generally okay for these folks).