Who says it's not? Don't the people living in a country have a right to decide what to do with it?
You can't just arbitrarily say huge chunks of planet are off limits because the people who fell out of a vagina there say so.
You can enforce it with guns and an ongoing culture as we see with the current state of things, but that doesn't make it moral.
Who says it's not? Don't the people living in a country have a right to decide what to do with it?