I'm so torn on this issue, I can't decide where I fall.
On one hand, I don't think governments should tell grown adults what they can or can't put in their bodies. That goes for food, drugs, or nutritional supplements. On the other, I think we should do far more than we already do to keep harmful things from kids. I don't know what the middle ground is... you can do whatever you want to yourself, but it's still a serious crime to sell it to someone else (especially a minor)?
The other sticky part is our public health system. If we are going allow people to do whatever they want with their bodies, should we still expect everyone else to pick up the tab? For instance, part of me still thinks that perhaps tobacco should be outlawed because of the health consequences. If smoking were illegal, smoking ANYTHING would likely be covered by that, bring us back to where we are with pot, just for a different reason. Maybe the answer is to treat health care the way other insurance is done -- deliberate acts of "bad health" make your coverage get cancelled. For instance, we have socialized insurance for cars in manitoba, and people can and DO get their coverage pulled for bad driving.
Pot is easier for kids to access than booze, exactly because pot is illegal and dealers don't check for ID.
If prohibition worked, I'd be all for outlawing booze and smokes. They cause a lot of harm. But, it doesn't work, people still get their drugs, just in a less safe way.
As for the medical coverage argument - far cheaper to provide treatment than to deal with the fallout of of not providing it. And with pot, the costs are insignificant, as a BC study showed - all of the social costs associated with pot were for enforcement. Tobacco, otoh, has very high medical costs to society.