The implication is that since America stole it from the Indians, we have no complaint now that its being stolen from us and absolutely no right to fight for the country at all.
Would they feel the same way if we were invaded by Russia? Or suppose Chinese warships anchored off shore and sent in thousands of military to secure the cities. Would the same arguments be used? Following the logic, it should be. If Americans have no right to America, it has no right at all no matter who the invaders are.
Recently Russian bombers approached the West coast and were chased off by American jets. Why? If we are all here illegally and have no right to claim this as our country, why bother chasing off the Russians? They have as much right to be here as anyone else.