We're crazy if we think this is just a 1st Amendment "freedom of religion" issue!
If only Hitler had declared Nazism to be a "religion," naive Americans would have permitted him to build "Nazi Temples" across America in the 1930s, staffed by youung Aryan "priests," (while stockpiling arms and explosives, and doing target recon).
Then they could have blasted the Horst Wessel song from loudspeakers, along with the "prayers" of Adolf Hitler.
ALLAHU AKBAR! = HEIL HITLER
MEIN KORAN = MEIN KAMPF
What if Muslims citizens of the US want to build a mosque?