CIA, MKUltra, and the cover-up of U.S. germ warfare in the Korean war (2022)
Biological weapons are not used by the US due to practicality, not morality.1. It's difficult to manufacture biological agents in large quantities.2. It's hard to store biological agents for long periods of time, since living things tend to die.3. It's hard to disperse biological agents over a large area. Spray tanks require flying at low altitude at slow speeds, or multiple deployments at high speeds. Munitions with bursters are problematic because the explosive burster tends to destroy much of the biological agent that you're trying to spread.4. It's easy to protect troops in the field from biological agents and all major countries maintain and exercise the capability to do so.5. Biological agents are slow acting and unreliable in their effect.Long after the Korean War, the Soviet microtoxin program overcame many of these problems. The Americans took a different approach and focused on improving nerve agents, with the most recent development (that I know of) being a multi-part agent called GB-2.