More than just being indiscriminate, chemical weapons actually pose a greater hazard to non-combatants than they do to combatants who likely have protective gear and treatment. Unprotected contact with most nerve agents resulting in agonizing pain, disfiguring and disabling injuries (from the solvents used in the delivery vector), and mass death. Vehicles and wind can carry deployed chemicals well outside the theater of combat, and under optimum conditions some substances such as BZ and VX gases can persist for weeks, especially if they are not exposed to rain or sunlight, which can pose a hazard long after combat is concluded.
Chemical weapons also pose a hazard in manufacture (from byproducts and release), storage (accidental release, damage in handling), and destruction (incomplete destruction, toxic residue). Release of Soviet archives has exposed numerous incidents of accidents and deliberate testing on human subjects, but it isn’t necessary to travel to the Evil Empire to find such incidents; the Army Chemical Corps performed many experiments on unaware subjects and the general public. Such tests are necessarily considered classified, and so the subjects are not even aware of potential health impacts.
As many chemical weapons are nerve agents using potent solvents, the potential for both genetic damage and detrimental epigenetic changes, which may cause harm both to the immediate victim (in the form of cancer, histone dysfunction, mitochondrial damage, et cetera) and to offspring. So the damage can last much longer than the environmental persistence of the toxic.
From a tactical effectiveness standpoint, chemical weapons just suck. Their latency against protected/mechanized troops make it ineffective at stopping attack, the lack of controllability in deployment may result in equal hazard to your own side, and the inconsistent decay period makes it a poor choice for any territory you intend to occupy, which effectively makes it a “scorched earth” denial weapon, denying safe use of the land for peaceable purposes for an indefinite period. For practical use in “lawful” warfare (that is, a property or access conflict between two states) chemical weapons have little use. As a tool to terrorize the unprotected non-combatant population and cause numerous casualties that create a burden upon the opponent, on the other hand, it is well-suited…and this is generally considered about as moral as arresting a criminal by taking his family hostage.
Whether war can every be truly “moral” in any practical sense of the word is another discussion. Clearly, when push comes to shove, even the right side is willing to commit grave atrocities against a civilian population in order to achieve their aims (witness the firebombing of Dresden and Tokyo, the bloody invasion of Okinawa, the strategic planning by both sides in the Cold War to deliberately cause devastating damage to civilian populations and infrastructure in order to debilitate the ability of the nation to recover, et cetera). Essentially immoral actions seem to be intrinsic in war. But having such weapons in an active stockpile and the use of them accepted in official doctrine certainly increases the likelihood of use even when the justification is questionable.
Stranger