Why do you think it's ideological? I was in agreement with you on the asymmetric warfare part, but I don't think there's anything irrational about using suicide bombers in an asymmetric campaign, nor do I think that Al Qaida is motivated by some sort of mental illness.
I don't think that suicide bombing is ineffective (so in that sense yeah it could be considered rational from the planning perspective), however i don't think the campaigns that are waged today are consistent with the values that people claim to espouse.
