The founders of this nation would disagree with you. The purpose of government, as explained in our declared independence from Britain, is to protect rights.
Libertarians can't justify taking such a position, and would slit their own throats by allowing a Mohammedan takeover by immigration.
I'll guess that your inability to understand why libertarians would have no trouble justifying keeping the likes of Atta and others out is that you don't understand the purpose of government in the first place.