It’s more than a WoD thing. Taliban use it for funding. They also like to come out in force to defend the crops when we destroy them. This could initiate direct combat instead of insurgency operations. Yet we don’t apply the pressure and try to play the game by the enemy’s rules.
The price would go down if opium was legal. No doubt it would be made up in volume - but if the whole country was growing opium legally it might mean less influence for the Taliban - farmers wouldn’t need their “protection” or markets.
If we’re getting out of Afghanistan in two years’ time it doesn’t make much difference in strategic terms anyway.