'If it's not religion, cat, what on earth is it about?'
In the case of the Paris hostage situations, it appears to be a small cell of close friends whipping themselves up in an isolated violent frenzy. When they mention religion it sounds nothing like Islam, it's taken one small part of Islamic teaching and stretched a point to such extremes it is no longer recognisable. To the point that they have completely crossed the line and they are perpetrators of horrible crimes. So it isn't about religion now, it is about the murders and atrocities they have commited; the laws they have broken.
As for ISIS, that's about power, land grabbing, ethnic clensing, war crimes and another, grander level of criminal activity. There is no excuse that can justify it and quibbling over religion is like fiddling while Rome burns.