Sometimes silent support acts as enabler to those doing the harm. Alas, views of the majority of muslims are not encouraging (i.e. views on issues whether sharia should be the law of the country, should apostasy be punished by death, etc.)
Besides, religious courts already exist in the US. For example, Halakha are religious courts run for Orthodox Jews, they exist in America and make many decisions on family law and civil disputes. But even among bigger groups, lots of disputes are dealt with within the religious community, Catholics have 200 diocesan tribunals, if you want to end your marriage and stay in communion, you pretty much have to ask for an annulment at a diocesan tribunal.
Lots more examples:
http://www.pewforum.org/2013/04/08/applying-gods-law-religio...