Not all the "muslims" who went to join ISIS started out as muslims.  You seem to prefer to gloss over that fact.  Quite a few of them were average white, christian kids who got sucked in by propaganda or simply had a desire to kill and wanted an excuse.  There's no fix for that.

Defeating ISIS won't end terrorism. Putting every Muslim person on Earth wouldn't end terrorism either, not that it's even possible. There will always be people eager to put on a mask and commit acts of violence. We can't pretend we live in a world that doesn't exist. 

Should security agencies and the police do their best to prevent violent extremism?  Sure.... and they do.  Does calling it ISLAMIC extremism help that process?  Not really.... although it seems to make you feel better.