ADDED: Uncle Jimbo makes the comparison:
Atta - Islamist extremist member of a death cult dedicated to the murder of as many people who disagree with their religious views as possible. Ringleader of plot to fly loaded airliners into the twin towers, White House and the Capitol building. Succeeded in killing almost 3,000 people.The idea is that they are completely different. I agree that they are different, but I wanted to move you to examine yourself. Many of us look at that picture of Mohammad Atta and think we can see evil. That is one of the most loathsome photographs in history. And then there's Ivins, smiling, nerdy, twinkly... we'd never pick out that face as a terrorist. We need to become skeptical of our own ability to see evil in a photograph.
Motivation - A far too common interpretation of Islam and a desire to put the entire world under the totalitarian, iron sandal of Sharia law.
Ivins - A pitiful nerd scientist obsessed with a sorority whose member had (quite obviously correctly) spurned his advances. Mentally unstable, increasingly more deranged, begins mailing packages and letters under assumed names. Eventually goes all the way around the bend and sends anthrax to a number of places killing five.
Motivation - He's a freakin' nuttah, who eventually snapped and indulged his mania and his need for employment by creating a domestic terror incident.