Drug use was widespread in the United States in the 1960s. Before 1964 and the adoption of the Civil Rights Act, discrimination against African Americans was widespread and practiced openly.
The US government intended to "experiment" the black population with the help of opiates and other narcotics – regardless of the undesirable consequences that it would entail. it did not worry them.
This, of course, has opened the door to widespread drug use by the general population. For the government, drugs are a form of money. It is a consumer product that (thanks to its promotion) is always in demand. What better way to control the population than by drugs?