"Blowing your people up with high explosives is allowable, as is shooting them, or torturing them," wrote Dominic Tierney in a piece for The Atlantic. "But woe betide the Syrian regime if it even thinks about using chemical weapons!"
The rule of murdering your population, Tierney cheekily wrote, is don't use chemical weapons.
As Stephen Walt, professor of international affairs at Harvard University's Kennedy School of Government, pointed out in a piece for Foreign Policy: "Does it really matter whether Assad is killing his opponents using 500-pound bombs, mortar shells, cluster munitions, machine-guns, ice picks, or chemical weapons? Dead is dead no matter how it is done."
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And it's that point that many find difficult to reconcile. Why are the deaths in Syria of over 1,000 people by chemical weapons deemed more horrific than the killing of 100,000 by conventional artillery?
In a piece for Foreign Affairs titled "A Taboo Worth Protecting," Mount Holyoke College professors Sohail H. Hashmi and Jon Western argue there is a significant difference between using conventional and chemical weapons.
"They're weapons of mass destruction, they’re weapons of indiscriminate destruction and they’re weapons of prolonged destruction," Western said in an interview with CBC News.
"They really can kill a lot more people in a very short period of time than most conventional weapons."
Also, depending on the weapon, they can inflict suffering for decades,including long-term medical effects such as birth defects higher rates of miscarriage and cancer, Western said.
The ban on chemical weapons followed the First World War, where at least a third of the munitions used were chemical weapons, noted Richard Price, University of British Columbia political science professor and author of The Chemical Weapons Taboo.
The Geneva Protocol of 1925 prohibited their use and the Chemical Weapons Convention of 1993 added a prohibition on their development, production and stockpiling.
"It's not about simple numbers," Price told CBC News. "The reason that chemical weapons have been banned and efforts to curtail them was a fear they could create really mass casualty events against civilians in particular.
"And you have just seen by this attack [in Syria] how they can easily do that.This was a significant attack but it wasn't a massive attack with aerial bombardment. And you could just imagine the scale of the slaughter in a really widespread series of attacks."
But Jonathan Mueller, a political science professor at Ohio State University, doesn't believe a distinction should be made between weapons.
"I’ve never been very comfortable with the idea that killing people with one way is better than killing with another way," he told CBC News in an interview.
In a piece he wrote for Foreign Affairs titled "Erase the Red Line," Mueller said in the First World War, chemical weapons were actually found to be humane compared to conventional weapons. Although they did cause a large number of casualties and took men out of action, only a small percentage of them actually died, he said.
He said questions have also been raised about the number of Iranians killed by gas during the Iran-Iraq war. Of the 27,000 gassed, Iran has said only 262 were killed.
Western agreed that chemical weapons have proven not to be very effective on the military battlefield, but "what that means then is when they're used, they're often used solely as a weapon of terror.
"Militaries can often employ counter-measures when they're used, civilians can't So they're often going to disproportionately kill civilians," he said.
But Mueller said that even Baghdad’s chemical attack on the Iraqi Kurdish town of Halabja in 1988, where 5,000 people were killed, may be an overestimate, coming from Iranian officials eager to boost the numbers of dead. Other reports have placed the death toll from 400 to under 20, Mueller said.
"What you’re doing is arguing esthetics, the esthetics of death," Mueller said. "People feel more revulsion for this kind of killing and that's just the way it is.
"Having somebody with their arm blown off with shrapnel and gradually declining and his eyes glazing over hours and then succumbing to shock is also horrible. The key thing is to get rid of murder rather than a particular weapon."