I usually speak ill of the concept that "chemical weapons" are especially horrible, as military weapons go, and put "chemical weapons" in quotation marks since, obviously, trinitrotoluene (TNT) and its descendants such as C4, white phosphorus, napalm, and, for that matter gun powder are based in chemistry.
Still, poison gas is
special. It is special not because it's a weapon of mass destruction or
"a poor man's a-bomb" but because it's a small-time oppressor's
Cossacks or NKVD or Waffen SS or Gestapo, or gun boats or US
cavalry in the West during the Indian wars — the "nadir" of US Army
history according to my old US Army history of the US Army — or whatever
the British would have called the army units assigned to "administrative massacres" in the old Raj if the British had implemented that particularly obscene scheme to maintain control in India.
gas is special because it allows small-time dictators to use old
technology to perform with "surgical precision," relatively speaking,
punitive and terror operations that major powers like the US can now do
with cruise missiles and drones.
gas is better — i.e., superior for getting the evil job done — than
Hellfire missiles or a gunboat attack, or even sending in the Cossacks.
gas isn't a weapon of mass destruction in large part because it isn't a
weapon of destruction at all: it kills or at least horribly hurts and
incapacitates people while leaving infrastructure intact. Moreover, gas
kills people with potential deniability, or at least more deniability
than sending in the Marines to kill Filipino insurrectionists who wanted
the Philippines for Filipinos — or the Cossacks and Black Hundreds into
some shtetl Czarist authorities wanted to keep in line. (More
loosely-controlled domestic terrorists like the Ku Klux Klan also
allowed deniability, but that's a somewhat different story, including
the point that a lot of US politicians into my lifetime wouldn't bother
denying supporting the KKK.)
Cruise missiles and drones, like 19th-century
gunboats, allow major powers to punish weak states by launching lethal
attacks against them from a safe distance. Such attacks don't kill off
many "enemies" — the quotation marks here are inherited from Joseph
Conrad's Heart of Darkness —
but they also don't risk one's own fighters. Using poison gas against
"soft targets" such as one's own civilian population is also safe.
like gunboats, cruise missiles, and drones, for such reasons poison gas
is tempting: very tempting since poison gas is relatively cheap and
within the budget and technological or shopping abilities of all but the
least of dictators.
let us all support the international conventions against poison gas. At
the same time, though, let us avoid making fashionable again the whole
idea of gunboat diplomacy: making "rogue states" behave by punishing
them by killing off some of their people, from a safe distance.
The Great Power arrogance of the 19th century was very bad in itself, and in the 20th century produced results that were horrendous.