Mass graves in Iraq

The news today is that a mass grave containing "dozens" of bodies has been found in Karbala, Iraq, part of the "as many as 30,000" (note the phrasing; when is the last time you attended a demonstration where the press reported the maximum possible number by saying "as many as 300,000 demonstrators protested the war today"?) Shia who were killed when their 1991 revolt against the Hussein regime was defeated. Having just watched "Hotel Rwanda" last night, I'm hardly going to speak out in favor of mass killing of innocent people as a tactic in fighting a civil war (or suppressing a revolt, depending on your point of view). The question, to which I cannot find a definitive answer, is who were those "30,000" (or whatever the correct number is) people?
It is a fact that rebels had seized control of Najaf and Karbala, so this was definitely a serious revolt. How surprising would it be if 30,000 people were killed in fighting a civil war/revolt? In the U.S. Civil War, in a country with a population of 31 million (i.e., comparable to that of Iraq), 200,000 were killed in battle, with far less lethal technology (although also less effective medical care) than available at the end of the 20th century. Thousands, sometimes more than ten thousand, were killed in single battles.

It is also a fact that there were other mass graves in southern Iraq, which were quite fresh at that time:

On the "Highway of Death," the American "Turkey Shoot" had killed thousands, perhaps "as many as" 30,000 (although most estimates are just "thousands"), retreating Iraqi soldiers, not to mention the literal mass graves created when American bulldozers buried hundreds or thousands of Iraqi troops alive during their initial attack. The "Highway of Death" (the Basra Road) extended for seven miles; just imagine the picture above, repeated nearly ad infinitum and definitely ad nauseum for seven miles worth of death, defenseless, senseless death from the air. However the 30,000 Shia died, and I can find virtually no information on the subject, it seems highly unlikely their deaths were any more brutal or morally repugnant than the ones that came at the hands of Americans.