Yes, in absolute terms we can but the current reality is different in our fight with ISIS. I think it's stupid to ban just using religion even when it's legal.No! There is clear precedent to exclude anyone from this country, for any reason whatsoever. No one has a right to immigrate to the US, and the US has the absolute right to allow, or deny, immigration to anyone for any reason.
Otherwise, what is the purpose of borders, or the concept of nationality?