Well said HiLo. I think we're all trying to understand the mindset of the terrorists. I expect the Inca had the same sense of horror when the Conquistadors arrived. All religions have their ruthless fundamentalist factions.
I reckon it boils down to a certain type of person who is willing to inflict pain, torture and death (psychopaths?) for some religious or political ideal. Many of us hold strong beliefs, but would never consider for a moment hurting innocent folk like this. It must take some power of self-motivation to put together a bomb and set it off among passers-by. Are they mentally ill in some way?