We've heard a lot about the conflict between Shia and Sunni Muslims in Iraq, but what's the difference? It appears to come down to one essential question.
The Shia say that Imam must be appointed by God; that appointment may be known through the declaration of the Prophet or the preceding Imam. The Sunni scholars say that Imam (or Caliph, as they prefer to say) can be either elected, or nominated by the preceding Caliph, or selected by a committee, or may attempt to gain the power through a military coup (as was in the case of Muawiyah).
The Shi'a scholars say that a divinely appointed Imam is sinless and Allah does not grant such position to the sinful. The Sunni scholars (including Mu'tazilites) say that Imam can be sinful as he is appointed by other than Allah. Even if he is tyrant and sunk in sins (like in the case of Muawiyah and Yazid), the majority of the scholars from the schools of Hanbali, Shafi'i, and Maliki discourage people to rise against that Caliph. They think that they should be preserved although they disagree with the evil actions.
The Shia say that Imam must possess above all such qualities as knowledge, bravery, justice, wisdom, piety, love of God etc. The Sunni scholars say it is not necessary. A person inferior in these qualities may be elected in preference to a person having all these qualities of superior degree.
Saddam is/was a Sunni, so his supporters didn't think it necessary for him to be sinless -- or particularly knowledgable, brave, just, wise, pious, or loving. Lucky for him, I guess.