We have done it with Jewish religious courts for years and i'm sure followers of all religions or groups ask their leaders to arbitrate on occasions. They are unfair but I don't see what banning them would achieve. Most are apparently unofficial and therefor if they were banned, they would carry...
Why?
If someone is unhappy with what happens in a Sharia Law court, they can still use all legal means open to anyone? (just like they have been able to in relation to jewish religious courts for centuries).