[slickQ]

Growing poppies has been consistently profitable for decades and is likely to remain profitable for the foreseeable future as the demand has yet to decrease.

It is true, however, that as the supply increases the likelihood that some consumers (namely addicts) won't be able to purchase any future batches increases as well (due to overdose, loss of income, etc). The market will likely reach an equilibrium eventually. Increases in supply have been met with increases in sales so the equilibrium hasn't been reached. This hasn't been a relevant consideration so far and there is no indication that it is now relevant. As such, it is hardly irrational or dumb to grow poppies at the moment.

The morality of the practice is another concern entirely. It is notable, however, that they do have legitimate medicinal applications.