Not nearly "all" nations are created illegally. Try the Czech Republic and Slovakia, for example. And what about the Algonquin Nation, were they created illegally?
While you do offer good counterexamples, these are more the exception than the rule
"All" only requires one counter example. People should really say something other than "all" unless they really mean "all".
Your brain should not work as a compiler, when everything must be 100% strictly correct on the language syntax to be considered valid.
People shouldn't use absolutes when they don't mean an absolute. It is not about 100% strictness, its about understanding what someone is saying. The "STOP" sign actually means stop, not maybe (that's "YIELD"). In other words, don't get pissy when you use absolute proclamations and others call you on it.