Practicing Nazism during WWII was probably not too legal in the UK and US.
We should take the exact same stance towards Mohammedanism.
Not all Moslems espouse the ideology of the Islamists like al Qaeda. Again, if religious freedom means anything, it is that people are free to practice their religion so long as it does not harm others. If individuals are engaged in fomenting or preparing violent acts of terrorism, then by all means, throw the book at them. Proscribing an entire religion is not narrowly-tailored.
We already have.
Look up the procedings of the New York State Supreme Court for the year 1892, I beleive, and see that islam is not to be considered a "religion" to be granted Fist Ammendment protections any more than one of the chicken-butchering or virgin sacrificing "religions" of the world.
'Course, PC liberals conveniently ignore things like that.