Stacey,
Obviously, you must have missed what I said. Here! I'll paste it for you!
an opinion based on factual evidence and historical precedence.
I put "historical precedence" in there for the exact reason you mentioned, ie, there is no way to show that "militant nationalism" is wrong using scientific methods.
So, there you have it -- historical precedence, eg. the Nazis, authoritarian communisim, genocidal tribalism, etc... Does this clarify things for you?
Bradley