I know of no evidence for that proposition, and can offer counterexamples. One would be the Interfaith Drug Policy Initiative, made up of Protestant, Catholic and Jewish clergy, which supports drug law reform: http://en.wikipedia.org/wiki/Interfaith_Drug_Policy_Initiati...
You're correct that historically, "anti-vice" austerity linked to Protestantism was a powerful force in American society. But the Prohibition era began nearly a century ago, and society may have changed in one or two teeny tiny ways since then. Like the 1960s? Plus the easy availability of Internet porn should give the lie to the concept that "anti-vice" religious mores are dominant. :)
Congressmen still show a reluctance to reverse already existing laws regulating drugs - it's easier to get them to pass new laws than reverse existing ones unless the existing ones are truly broken.
In the case of religion, you're confusing a transparent and rarely-invoked justification with the actual reasons for the WoD. In the case of politics, you're confusing the mechanism for prohibition with the actual reasons.