a) If advancedatheist was the leader of the US, and people would follow him, he probably could conquer or kill a billion through technological superiority without too much difficulty.

That basically assumes war is only about direct fighting strength but not about ideas. In practice winning hearts and minds is important to win wars.

The framing of a cultural war helps organisations like IS immensely in their recruiting efforts. Speaking about how Islam is evil in public in a forum like this has a real effect on the conflict.