One doesn't need to assert any natural rights. Once can make a completely utilitarian case for the decriminalization of controlled substances. In fact, nearly all available evidence points in that direction -- it is increasingly hard in w a world full of data to make the case that criminalizing substance use offers any utilitarian benefits at all. It makes the drug market a more dangerous place, controlled by violence. It destroys the lives and the communities of substance users by incarcerating them for long lengths of time. Etc etc etc. I don't need to lay out all the facts here, they are plain to see for anyone who looks into them.