Chemical weapons are viewed with horror in the Western world based on the experience of the western front of World War I:
The current global—and Congressional—debate about whether to deploy force against Syria for its use of sarin gas on civilians will depend, in part, on whether the reasons for a post-World War I agreement banning the offensive use of chemical and biological weapons continue to be honored.
The 1925 Geneva Protocol did not focus on World War I's terrible new 20th-century technologies that made 19th-century military tactics obsolete and led to mass slaughter: advancements in barbed wire, machine guns, and artillery led to incomprehensible and horrible effects on combatants. It was the impact of gas use on both the Western and Eastern fronts that led to the prohibition on chemical and biological warfare, even though it had led to only about one percent of the deaths there. The protocol viewed gas warfare as different from the other methods of mass killing, and banned the use of "asphyxiating, poisonous or other gases" as well as "bacteriological methods."
But the "global" prohibition is purely the result of Western nations with that view of chemical weapons dominating the global system.
The rest of the world doesn't share the view because they did not experience the trauma of World War I that would have been horrible even without poison gas.
Consider the use of gas since World War II. (And even Italy away from the western front used gas to invade Ethiopia between the wars; and in World War II, Japan used them--just not against Western states that could retaliate in kind.) The instances are by states not-involved in the brutal western front and so lacking the instinctive revulsion at chemical weapons use. (Although I don't count Argentinian use of tear gas as chemical warfare.)
It is quite possible that chemical weapons are the "scapegoat" for the bloody, stalemated horrors of the western front in World War I, where chemical weapons were actually a minor factor in the death toll.
So other states that the West may face will not fear or be repulsed by chemical weapons use the way we feel. (Although if the fighting got hard, would that lingering institutionalized horror give way to a resolve to "do what it takes" to end the war?)
In theory, we think that the threat of nuclear weapons is a deterrent to enemy chemical weapons use.
But is that true if the opponent doesn't share the thinking of the West on chemical weapons use?
Would an enemy use chemical weapons on our troops, not believing it is anywhere near the same level as nuclear weapons?
Would we actually use nukes--and remember that we continue to destroy our chemical weapons as we agreed to eliminate--if our forces are hit with chemical weapons? Or do we need to think about whether states that don't share the Western revulsion over chemical weapons will use them on us if they get the chance?
And where does Russia fit on that issue? In the Cold War, we certainly feared they would liberally use gas if they attacked NATO. I sure practiced suiting up a lot in my limited time in uniform.
