There is always an element of the police state inherent in the nanny state. If your health care is public business, then it’s everybody’s business what you eat, drink, and smoke, whether you get enough sleep and exercise, etc. In the context of cradle-to-grave social programs, telling people that they cannot smoke marijuana may be entirely reasonable, a question of cost-benefit analysis. But that view involves forsaking, or at least minimizing, any real and robust sense of privacy and individual autonomy, the idea that the state simply does not get give you certain kinds of orders, regardless of the cost-benefit analysis.
In a sense, that is the fundamental difference between the progressive view and the classical-liberal view: For the progressive, everything is in the end a cost-benefit calculation, and there are few if any permanent principles limiting what public policy can do if the payoff is sufficient to warrant it. For the classical liberal, some things are beyond that sort of analysis, and beyond democracy, for that matter: We’d still want free speech even if a thousand Brookings studies proved that it imposed social costs outweighing its benefits, even if 51 percent, 65 percent, or 99.99999 percent of the electorate wanted to get rid of it.
People on the conservative-libertarian end of the spectrum see the drug question as being more like free speech than like the question of whether the top income tax rate should be 35 percent or 39 percent. In general, we tend to see many more issues as belonging in that category, whereas progressives see more issues as being matters for cost-benefit analysis.