You said -- "What you suggest even using your number is that we kill 1.2 billion people."
You can avoid indiscriminately killing 1.2 billion people. You simply need to destroy the religion of Islam by destroying all their holy sites all over the world -- at one time. Destroy all the Mosques here in the U.S. Make the religion illegal. Kill all the clerics that teach terrorism as a means for spreading a religion (or for another means, for that matter).
Do that and you won't have the *basis* for Islam any longer. It will go away.
Regards,
Star Traveler
P.S. -- There will be as much sqawking about that as there has been for the U.S. going into Iraq and for supporting Israel. Just put up with it and be prepared to fight any immediate effects of it. It will die down in short order -- once the reality of all their religious sites being destroyed sinks in. And once they realize how impotent their so-called "god" (Allah, aka Satan) is -- they'll abandon him.
That wouldn't make it go away any more that destroying every Scientology church would make Tom Cruise go away.