Free Markets and Drug Prohibition

I have a philosophical question for conservative drug warriors: Why do you believe rational individuals should not be allowed by government to put any foreign substance they wish into their bodies? Put another way, why do you believe the state has the right to dictate to rational individuals what they can and cannot put into their own bodies?

You cannot call yourself "free-market" and believe in drug prohibition (and other types of prohibition that fall outside the Law). It is intellectually disingenuous to do so.