Here is a good reason and a start, others will explain more I'm sure.
http://www.michaeltotten.com/Inside some of the cells are messages carved by children into the walls. I was ten years old. But they changed my age to 18 for execution. Dear Mom and Dad. I am going to be executed by the Baath. I will not see you again.
Those were scratched in the walls of one of Sadam's prisons that raped women and killed children.
The whole world though he had a weapons program. Yes, apparently we were wrong but it was widely felt that he was a threat.