No need for conspiracy theories when the facts are so readily available.
If you really think that America’s marijuana prohibition had nothing to do with racism, then digest Harry Anslinger’s Wikipedia page[2].
Anslinger was an opportunist lawman who made a name for himself during Prohibition and latched onto America’s racist fears of blacks and latinos to cement his legacy and influence. Ironically his early stance was that prohibiting marijuana was absurd, until alcohol was legalized and he neeeded a new way to grasp onto relevancy.
1. https://en.wikipedia.org/wiki/Three-fifths_Compromise?wprov=...
2. https://en.wikipedia.org/wiki/Harry_J._Anslinger?wprov=sfti1