"Always"? Pretty sweeping, categorical assertion. Voters' politics is based on interest, identity, and values. The latter two often run counter to the first (e.g. poor whites in the Republican Party, blacks in the Democratic Party). Blacks suffer disproportionately from Drug Prohibition, but many are religious and culturally conservative, and would like to see the death penalty for drug dealers (assuming the police could be trusted). They blame the drugs, not Drug Prohibition.

Lots of your anti-prohibition activists are wealthy progressives and libertarians who, like me, like David Simon, have no personal stake in the outcome.