“It would be street warfare... no mosque would be safe, and there’d be a lot of crossfire damage.”
Yes, but there might be a downside...no, I can’t think of any.
I’d say, the downside is encouraging a secular bunch of patriotic German brownshirts—who knows where that would go. It went down a pretty hairy path between WWI and WWII. On the other hand, repressing the normal civic immune system and letting Islamists run riot seems even more unwise.