Sorry friend but you need to up the intellectual level of your argument.

Destroying a crop is not the equivalent of destroying the farmland itself. Taking out a key piece of the irrigation system does not mean that the whole irrigation system gets to be destroyed... just placed beyond use (if necessary) until they play ball.
So, rather than permanently despoiling the land, we will simply remove part of the irrigation system, destroy planted opium, and ensure that no one repairs said irrigation system or replants the opium.

I am not sure how doing so changes any of what I said before, except that this solution will be more costly in terms of manpower requirements and technical expertise.

Can you address how doing so will at least assist in defeating the insurgency or significantly degrading opium supply to the point where the benefits involved would outweigh the costs?