I'm glad that as an American, I can own vastly more than enough firepower to blow away anyone trying to mess with me or my family on my property. Come at me Achmed.
That being said, if two (or more) individuals have a dispute and willingly choose to go to one of these Sharia courts to have the dispute decided, that is their business as long as no one else's liberty is being violated (aka, someone who didn't consensually come to the Sharia court). None of us have legitimate authority to force people to bring their disputes forward in a government court. Individuals should be free to mutually, consensually solve their disputes as they see fit.