It is an ingredient. Eric Hoffer's _The True Believer_ is a good sketch of the phenomenon. Among the disaffected, some will latch onto any available dogmatic belief system. As long as radical Islam is in the news, and is accessible, some among the disaffected will choose that path.
Not all dogmas result in blowing yourself up in crowds, or setting off bombs or gunning down people in theaters. Doesn't it make sense to preferentially attack those dogmas that bring out, at present, the worst characteristics in their adherents?
It would be great if our foreign policy in the past 1.5 (or 3, or 5, or 7) decades hadn't been a disaster and promoted unrest in the region, because that undoubtedly increased the seriousness of our current situation. We (by that I mean our leaders who make foreign policy and military decisions) should try to learn from history and not repeat the same mistakes, although they all (no matter their politics) seem to do a very poor job of that. But the question of why radical Islam is such a problem now is irrelevant to the question of whether we should fight radical Islam. It's not a very reasonable thing to conclude that because we're partly responsible for the rise of radical Islam, we should do nothing and let it conquer the world if it wants.
