This has nothing to do with an abstract notion of morality.

In our society, we look out for each other, if somebody is in distress, e.g. hurt on the side of the road, we help him, call an ambulance, he gets medical help.

The fact that society makes huge efforts to save and cure people requiring medical attention, is at the root of the taboo on substances (or behaviors) that are unhealthy. Otherwise that would be a pure waste of resources for the society.

At least that was the theory. In practice, you are free to drink booze until you pass out...