This is a law system. The US is not beholden to it. They however can use concepts of it. There is no law against things like Mormon… this is semi similar. They are not allowed to have like formal you must do this or else is all. They can say that you are not welcome on there community.
This is a little like if you show up drunk at Mormon church on Sunday once and then do it again making an ass out of yourself they will say your not welcome at lest until you are approved back by the people that choose this.
This is no different then a business refusing service to someone as well to in these ways. So this in particular is how it is seen the same in laws.
So no they can’t use Sharia as the law is the land however they can use it as guidelines. If someone feels they been unfairly treated the institution or people can be sued though. This where it is not able to in-force laws they make up.
So there is interpolation factors it is like Mormons interpretation of the Bible is a hair more strict then others. This does not make them bad people. Never met a pushy one in a bad context. This where they do not push their views to far I believe but do not be a member and disrespect things like I said above is all.
It is about the same like do not go to a Islamic holy gathering with soup with bacon to feed people them not knowing it. This would be asking for provoking them in this aspect. This would be a reason that a court of law would understand them banning them and not able to sue. Now if they beat them although this is caused by something it is still not ok but is factored into things what they did in this way. Things like if they saw them doing this like about it put things in snicking and they tackled them and they where injured are a lot different then if they took them outside and beat them for 10 mins.
This is what they look at is all.
Would not blame Islamic people for banning people if they did this ok.
These 2 examples make the same sense in my mind.