Social Control

In Hallucinations: Behavior, Experience, and Theory (1975), senior US government researchers Louis Jolyon West and Ronald K. Siegel explain how drug prohibition can be used for selective social control:
The role of drugs in the exercise of political control is also coming under increasing discussion. Control can be through prohibition or supply. The total or even partial prohibition of drugs gives the government considerable leverage for other types of control. An example would be the selective application of drug laws… against selected components of the population such as members of certain minority groups or political organizations
Academic Noam Chomsky argues that Drug laws are currently, and have historically, been used by the state to oppress sections of society it opposes:
Very commonly substances are criminalized because they're associated with what's called the dangerous classes, poor people, or working people. So for example in England in the 19th century, there was a period when gin was criminalized and whiskey wasn't, because gin is what poor people drink.