What if the person doesn't want to quit? What to take into your body and how to regulate your health are deeply personal choices. Why not just let people make them?
I didn't remark on that but I'll entertain your comment: I think it's about having the facilities to educate people about the effects, and help them in rehabilitation if they prefer to.
I think we already do a pretty good job at this, don't you? Drug awareness education in one form or another has been part of the curriculum since the 19th century.
> help them in rehabilitation if they prefer to
We have lots of NGOs that are setup to help drug addicts. Are they not doing a good job?