This chapter traces the reasoning behind the widespread advocacy of chemical weapons during and after World War One by military officials and scientific experts—with Fritz Haber and John Burdon Sanderson Haldane prominent among the latter. The fact that an estimated 1% of military deaths and 6% of military injuries in the war were due to chemical weapons inspired the notion that chemical weapons were, in fact, humane. The universal abhorrence of chemical weapons as manifestly inhumane is more recent, as is their classification as weapons of mass destruction. That favorable views of chemical warfare were once prevalent is barely comprehensible today and, unless contextualized within the mode of thinking of experts at the time, appears absurd. The elimination in 2023 of the declared chemical arsenals by all 192 parties (representing 98% of the world’s population) to the 1993 Chemical Weapons Convention (CWC) reflects the current attitude toward chemical weapons worldwide. However, chemical weapons have meanwhile been superseded by what Haldane considered unfeasible in 1925, namely nuclear weapons. Consequently, chemical weapons had been relegated to the sidelines as “poor man’s atomic bomb.” What Haldane did get right, however, was that, if feasible, nuclear weapons could upend organized life on the planet. We conclude by noting that our consensual coexistence with stockpiles of nuclear weapons should be judged as beyond absurd.