Also wrong.
Henry Anslinger, the man responsible for modern-day prohibition, was backed by Lammont du Pont, of DuPont chemical company. He had a financial interest in illegalizing HEMP, a direct competitor to DuPont's newly developed Rayon.Since anyone could grow it, it was a threat to their sales.
FOLLOW THE MONEY.
Of the 3 species of cannabis (sativa, indica and ruderalis), ruderalis was an industrial power-house and direct competitor to synthetic fabrics. Sativa and Indica were sold in all sorts of medicinal tinctures at the time (pre-1930's) which of course directly competed with the emerging pharmaceutical industry, of which DuPont was a part.