Prowler's right about one thing. You can't kill an entire faith.
What you CAN do, however, is decimate certain segments to the point that you create a leadership void. A void into which less extreme voices can intercede and hopefully reshape the direction.
With Islam though, I don't know if that's possible. It's not a religion of peace and assimilation. The stated mission of the religion is to either convert or kill. Even those who claim to want to live in harmony have that at the core. One day allah and his laws will rule over us heathens.
Kill ISIS. Beat the entire religion back to the point it takes hundreds of years to recover. That's what we should do. Modern day crusades.