I'm reasonably sure the author is just making this up. As a US citizen you have wide discretion on where you live, even extending to several other small nations that have signed agreements with the US.
If you're renting or selling property, most of the discretion that used to be afforded to buyer's is now outlawed. But it would require someone willing to pursue a case if they felt they were not sold a home because of their race or whatever.
Funny, this comment reads like something Commander Data would say in Star Trek. He would always respond to the letter of what was said, while completely missing the human context.
It fascinates me that someone who read the parent comment could actually think it was about the legal rights of US citizens. You might as well be claiming it was about hummus :)
They could legally move there, but they would be shunned from the community, and indeed it may be hard for them to find someone willing to even sell them a house.
I'm pretty sure GGP did not mean they literally could not move there. They could move there and be shunned by society if that's what they are into. But why else would you want to be there except for the society?
If you're renting or selling property, most of the discretion that used to be afforded to buyer's is now outlawed. But it would require someone willing to pursue a case if they felt they were not sold a home because of their race or whatever.