The truth is that our perceptions of marijuana—and in fact all of our drug laws—are based on early 20th century racism and “science” circa the Jim Crow era. In the early decades of the 20th century, the drug was linked to Mexican immigrants and black jazzmen, who were seen as potentially dangerous.
Harry Anslinger, the first commissioner of the Federal Bureau of Narcotics (an early predecessor of the DEA), was one of the driving forces behind pot prohibition. He pushed it for explicitly racist reasons, saying, “Reefer makes darkies think they’re as good as white men,” and:
“There are 100,000 total marijuana smokers in the U.S., and most are Negroes, Hispanics, Filipinos and entertainers. Their Satanic music, jazz and swing result from marijuana use. This marijuana causes white women to seek sexual relations with Negroes, entertainers and any others.”
The main reason to prohibit marijuana, he said was “its effect on the degenerate races.” (And god forbid women should sleep with entertainers!)