[gjm11]

There are something like a billion Muslims who treat the Qur'an and the sunnah with equal reverence but somehow manage to get through their lives without beheading anyone or pillaging any cities.

And there are plenty of people who have been screwed over by US foreign policy but who, again, somehow manage to refrain from committing atrocities.

Terrorism generally seems to spring up where there is both a big political grievance and some kind of ideological foundation to hook it onto. That's not an absolute requirement (e.g., I don't believe the Tamil Tigers had any ideology beyond their nationalism; on a much smaller scale, the occasional cases of Christians blowing up abortion clinics aren't very political) but generally that partnership is what does it.

And when that's the case, it's misleading to blame the terrorism exclusively on the ideology or exclusively on the political grievance.

Groups like IS and al Qaeda, so far as I can tell, really truly do believe that what they are doing is justified by Islam; and they really truly do believe that what they are doing is a necessary response to US intervention in the Middle East.