Many people seem to be operating on the basis that the enemy of my enemy is my friend. This is an assumption whihc entirely ignores the fact the OBL is an Islamist extremist, and Saddam is a Stalin-inspited secularist.
If there was a proven link, not just conjecture based upon innuendo built upon vague and inconsistant facts, this would make the invasion of Iraq just as justifiable as the invasion of Afghanistan.