In cases like these, I don't know how you can distinguish between the mental illness and the Islamist extremism (or whatever form the extremism takes) - they seem to have been intertwined in the minds in question. As further information emerges, perhaps neater conclusions can be drawn, but I don't see it so far.

There seems to be a thought in some quarters that because these guys were more or less crazy, their political/religious/terroristic motives are inconsequential, and in fact, should not be spoken of. I feel that   because Islamist extremism/terrorism is so prominent right now as an option for crazies, it needs all the more attention.