I don't think insulting muslims hurts in the GE to be honest. How many voters have met or know a Muslim in the US and then they turn on a TV and all the say is radicalism. Then you got liberals arguing over whatever 0.003% difference they have in ideology and it sets up the perfect storm.
I don't think being an open Islamophobe will hurt Trump, but I do think presenting harebrained conspiracy theories like this will.