You're forgetting about the angry, crazed imam Sayyed Muqtada al-Sadr and his militia. If this nut assumes power after the U.S. leaves Irag, Saddam's reign will be like the "good old days for Christians.
Saddam actually was better for Christians than were most leaders in the region. He treated Christians no worse than he did Muslims, and a good bit better than he treated Kurds.