Who can remember the crops that were lost to us for not fitting through this filter? Those with some value, but not enough to support their growth and protection? Perhaps they are grown in a garden here, a ditch there. But not on great estates on the choicest land.
It does not matter that a state prohibits the crop from being grown; the state, by doing so, only declares itself an enemy of the group of bandits who form to profit from the crop. While the state increases the cost of protecting the crop, and also the cost of growing and harvesting the crop, by doing so it also puts its resources behind increasing scarcity, hence the value of the crop (not every person may grow for himself). The prohibition of a valuable crop thus creates a valuable niche or tropism, which will necessarily be filled in an economy just as in nature.
(One problem with RICO and forfeiture laws is that it allows the state (declared enemy of the crop, foreswearing benefit from it which might entitle the growers to protection) benefits from the bandits' benefit of the crop. The state shares in the profits, and this creates a peculiar set of incentives with the state participants maximizing their benefit.)
Coca, poppies, and cannabis will all be grown in the absence of state prohibition, because they are sufficiently valuable in either case. Only the nature of the army of bandits called into being to protect the crops will vary. The state, when it declares a particular crop its enemy, presents a formidable enemy to any would-be protector of the illegal crop. But the army of bandits that protects illegal crops has an important advantage over the state army of bandits that prohibits illegal crops: it may be formed specifically for this purpose, and need not fit any other functions of the state. The non-state bandit army protecting an opium crop need not provide any expected function of a state, and hence dispenses with many of the limitations of a state. This army lacks the legitimacy and resources of a state government, but can operate leaner and with fewer practical restrictions. For instance, the open use of atrocity to create property rights through terror is rarely available to state actors, especially modern democratic states. If they commit atrocities, they may rarely do so openly, and hence it is more difficult for them to create terrifying reputations. The non-state army of bandits that necessarily arises to protect crops does not have this limitation, and may benefit from this advantage to the detriment of the people. If it is true that a bandit army that uses atrocity will be better able to protect and benefit from the illegal crops than an army that does not, then it logically follows, given a variety of possible armies, that the tactics of atrocity will be used.
Frequently, states highlight atrocities committed by their opponents as reason that they, the states, should be given more power. It is rarely pointed out that the state is ultimately responsible for these atrocities, as their commission follows with very few assumptions from the very prohibition of a valuable crop.