I don't disagree with you, but I think what you wrote only applies to fascism in a vacuum or a very late stage of fascism where all the outsiders were eliminated. Basicaly, if we're at the point where fascists started devouring themself it's already game over, because everything else is destroyed. And I don't like the sentence "Fascism will exterminate itself" because it implies all we need to do is wait (even though I don't think you mean that). Fascism needs a helping hand to achieve it's end goal (exterminating itself; please, don't ban me mods lol).

That mentality is surely broader than fascism itself. You see it in any hypernationalist state. Rome had "the barbarians." The British Empire had "the savages." Nazi Germany had "the jews." There is always an "other" when the state needs it. Unless you're painting a broader form of fascism, perhaps.