[jacquesm]

> ...

Yes, such a weapon will never be very precise. But since no weapon ever is (collateral damage) that doesn't mean it won't be used.

> And how do you prevent the bioweapon from mutating that specificity away?

You don't. But even that won't stop such a weapon from being used. Every weapon that man kind has been able to envision and create has been used. Not a single exception.

[eesmith]

You have presumed that this sort of DNA-targeting bioweapon could exist. We have lots of pie-in-the-sky weapon ideas that haven't been developed, like the Supersonic Low Altitude Missile. Why are you so sure that this bioweapon isn't yet another one of those?

Setting that aside, the hydrogen bomb has not been used as a weapon, only a deterrent.

Same for the neutron bomb (an "enhanced radiation weapon").

And nuclear depth bombs ("All nuclear anti-submarine weapons were withdrawn from service by China, France, Russia, the United Kingdom and the United States in or around 1990.[citation needed] They were replaced by conventional weapons such as the Mk 54 Torpedo that provided ever-increasing accuracy and range as anti-submarine warfare technology improved." says https://en.wikipedia.org/wiki/Nuclear_depth_bomb ).

"The United States Army Biological Warfare Laboratories weaponized anthrax, tularemia, brucellosis, Q-fever and others.[51] ... In 1969, US President Richard Nixon decided to unilaterally terminate the offensive biological weapons program of the US, allowing only scientific research for defensive measures." says https://en.wikipedia.org/wiki/Biological_warfare .

Have all those weaponized organism really been used as a weapon? Not to my knowledge.

These all sound like exceptions.