It would be excessively boring to give a detailed legal explanation of exactly what it wrong with no_hypocrisy's flawed comparison there, but suffice it to say the 'No Sharia Law' thing means it cannot be used as a legal basis of decision in US courts on American legal issues, not that it is prohibited for people to obey it in their personal arrangements as long as it does not interfere with anyone else's rights, whether that obedience is driven by positive faith, fear of the afterlife, or objective reason. In a given case, it might be relevant to explain customs or the understanding of the parties and be cited for that purpose, but not as binding law. The same is true of any other ecclesiastical law, Hebrew, Catholic, Wiccan, Mithran, Zoroastrian, or whatever.