He won't because atheists like him, see Islam as a neutralizing force against Christianity, they want Islam to win, so that they believe that then they alone can defeat Islam themselves, but they would be in for a very rude awakening should it ever get to that point.
That’s part of it. Anti-Christian leftists see Muslims as “the enemy of my enemy is my friend”, until it’s time to throw them under the bus, too. But by then it will be too late for the leftists...as the Muslims will have gained enough strength and numbers to take over. I doubt that we’ll be around to witness all that though. At least, I hope not.