Our Founding Fathers, in their often argumentative wisdom, set the Constitution up to keep government out of religion, not religion out of government.
In the case of islam, I do not consider that belief/control system to be a religion - rather it is a Theocracy, aimed at total control of thought, action, dress, abuse of women & anyone not professing personal subscription to islam.  Non-believers are not only not to be tolerated, they are to be officially abused, & eventually, killed if they do not hold with islam & sharia law.
Semantics is present in most arguments, so what do you call a "religion?"