You seem to assume (as many on the Left) that the US involvement is a critical factor here - that is, there would be no Islamist fundamentalism had it not been for the US support of that movement under the rubric of anti-communism.
I simply do not buy that assumption. First, it is logically flawed. Not every support amounts to creating a social movement. Henry Ford's birthday gifts to Adolf Hitler did not unleash Nazism and start WWII. Second, it is empirically inaccurate. It ignores the internal factors (such as the class structure and social institutions of the affected countries), whose effects are much stronger than any meddlings of foreign policy makers.
Without the assumption of the critical importance of the US policy in foreign developments, this whole "blowback" argument is a nonsequitur - nothing more than an ex-post facto rationalization, the "poetic justice" trope that might provide some emotional consolation to the assorted First-World haters, but otherwise explains nothing.
wojtek