> But I don't want a government having any opinion on what people put into their own bodies.
I agree with this in principle, but only to an extent. It's not the government's business to intervene when people fill their bodies with, say, ice cream, which makes them happy but has some health consequences borne by the individual. But on the other hand, the government should certainly not permit people to fill their bodies full of explosive substances like nitroglycerin, which might detonate when they are outside walking around public spaces, taking out innocent bystanders.
Hard drugs fall somewhere in between these extremes, because in addition to their first-order effects on the user's health and happiness, they also seem to cause second-order consequences on innocent bystanders. Under the influence of drugs, some users can become aggressive and violent, and lose control of and -- importantly -- responsibility for their actions. Under the influence of addiction, some users also resort to robbery or theft to fund their habits. Many also end up unable to care for themselves. Statistically, this occurs with enough likelihood that it's a predictable, although not inevitable, consequence of substance abuse. Punishing the crimes committed under the influence of drugs does not act as an effective deterrent. Much of the harm from hard drugs does fall on people with no direct relationship to the drug users themselves, and they will have a strong and legitimate self-interest in having these substances banned.