"They're so indiscriminate," says Don Borelli, a former FBI official now with The Soufan Group, a security consultancy. "At least there's some discrimination in conventional weapons."
"Modern weaponry, while it's grown more lethal, has also grown more precise," says Michael Rubin, a former Pentagon official now with the American Enterprise Institute. But chemical agents disperse to affect large numbers of people and "can produce horror for a lifetime."
Some conventional attacks do the same, he acknowledges.
But there's another reason that it makes sense to view a chemical attack as a reason for international intervention, Rubin says.
"We want to establish the parameters of warfare. If you don't, combatants will keep pressing the boundaries. Ultimately, the question is, should we have any boundaries in war or not?"
It's a slippery slope, he says. If a chemical weapons attack goes unchecked, what about some other form of weapon of mass destruction -- a biological or nuclear attack?
Some chemical attacks have gone unchecked. In the current conflict, chemical weapons are alleged to have been used on a smaller scale several times.
And Foreign Policy reports this week that says the United States, back in 1988, "helped Saddam as he gassed Iran."
Rubin said he doubts that. But either way, he said, "There's a fundamental question: Should we learn from our mistakes? If we did the wrong thing should we simply sit by the wayside and allow that to happen again?"
The United States and other countries, he said, want to "restore a stigma" against chemical weapons that was in place in the world's psyche "after World War I and Halabja."
Analyst: Chemical weapons' impact 'exaggerated'
Tony Cordesman, a former Defense Department official now with the Center for Strategic and International Studies, says the image people have of chemical weapons is often exaggerated.
"Chemical weapons attacks are not necessarily any more horrifying than the use of conventional weapons," he said Tuesday. And "the lethality has always been far worse on paper than in reality."
There are no definitive statistics on how many people were killed in Halabja, he says.
The prevailing image many people have is still from World War I, "which was the last really mass use of chemical weapons," Cordesman adds.
Tierney, in The Atlantic, suggests a "strategic self-interest" for the United States to oppose chemical weapons.
"Powerful countries like the United States cultivate a taboo against using WMD partly because they have a vast advantage in conventional arms," he writes. "... Washington can defeat most enemy states in a few days -- unless the adversary uses WMD to level the playing field."
Rubin rejects that argument, saying the U.S. advantage in weapons of mass destruction precludes any possibility of a level playing field.
And while the alleged previous, smaller-scale use of chemical weapons in the Syrian civil war were not enough to bring about calls for action, he said, "This is such a blatant example, we can't pretend not to see it."