The key word here is arbitration. Arbitration agreements are private contractual provisions agreed to by both parties. They are in all 50 states and are used often in business proceedings, most often in employment. Your TV judge shows are also a form of arbitration. This is a divorce case being settled under Islamic religious principles. That is their choice. It's no different than Catholic Canon Law annulments.
This is nothing more than a contract, and I'm glad we still live in a society where we can have private contracts governed by terms we agree on.
COnservatives apparently now oppose the rights of people to enter into private consensual contracts.