Although no enforcement mechanism will be perfect, the War on Drugs saves lives. As a whole, keeping drugs illegal reduces use. For that reason, drugs should continue to be illegal, including crop-eradication. Violence from drug trafficking would only be worse if drugs were legal, because the market would be larger. As a whole, crop eradication efforts are worth it.
Crop-eradication efforts are simply the US abusing its status as a superpower to damage the lives and livelihoods of people in poorer countries. Crop-eradication uses chemicals dangerous to the environment in order to kill plants which have been used by people for thousands of years as medicinal herbs. These plants are also sold internationally, so the loss of these plants affects the profit of poor farmers. Crop-eradication is just bad.