>> But the risk in 50 years of people saying "we should have known better" seems really high.

Well, we are just about 100 years after alcohol was legalized. We have lots of data on how horrible it is for out bodies, how many accidents and premature deaths it causes. But I hear absolutely nobody in North America talking about curtailing alcohol in any way. (The UK medical bodies have spoken out against alcohol use in recent years.) In fact I see advertisements for alcohol virtually everywhere. So no, I do not believe we will have a reckoning in 50 years about pot.