Like any other product drugs have supply and demand. By baning drugs the government only restricts its supply, government cant however, control te demand for them. Once the supply is restricted and the demand still the same, prices will rise which makes selling drugs a very good business.
Because the supply is drastically reduced (causing an oligopoly) the producers have more control over the price and consequently greater profits, which in its turn increase the incentives for selling drugs.
This business although very profitable, is also very dangerous, once you have to fight police. This creates incentives for them(who want to sell drugs) to be armed and violent. So instead of terminating the "drug - sellers" government only select the most violent sellers to be on the market.
This is how government creates incentives to the formation of violent cartels.
Bonus phase - A moral defense of the legalization
when something is compulsory it loses its moral status.
In order for some act to have a moral status (moral or imoral) the individual must have the option to act or not.
for example:
If you are forced to donate this act is not moral, bacause you didnt have the option to do otherwise, this act is now amoral (devoided of moral status). The same happens if you are prohibited from using drugs. In this case not using drugs in not moral anymore, because you didnt had any other option, this act (of not using drugs) becomes AMORAl. So when you fight drugs, you are not making a moral society, it's the opposite, you are making a amoral society.
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