Besides, I don't think this could ever be legal. There are laws in America (and in every western country) which prevents segregation because of race, sex or religion.
I am not judging but this is only a matter of playing with law. We have secret courts and secret law, so why would it not be possible?

It is only because of the ignorance of the people as to how to use the Preamble to the Constitution, and the 6th, 7th, and 9th Amendments.

Yes, that's what I thought. I'm not familiar with American law, but this can't be standard law preventing segregation, it's probably in the American constitution.
I also wonder how such a scheme could me implemented. Let's I'm flying to the US tomorrow, would there be a guy at the airport asking everyone if they're muslims, and send them back right away? What if someone lies? How to check? Will you have to eat a slice of bacon to prove you're not muslim?
That's all right with me, I like bacon.
Select groups of people certainly can be constitutionally barred from entry, curfews set on them, and other restrictions. There are Supreme Court cases on this matter.
And as far as I'm concerned, if you like bacon you should get in.