I doubt your first bet but whatever. Go ahead and link that information and then I'll believe it. The deaths by drug OD is gaining on the HD numbers and it is impacting a younger demographic.
Was my "original justification societal cost"? I don't recall that but either or both are appropriate since no man is an island.
Oh, there is a societal cost. The family and friends of the younger person saddled with addiction, the theft and other criminal behavior to obtain the drug by the "victim" as well as their suppliers, the cost in intervention, emergency responses, medical care, etc., etc., etc. Now you may argue that it is the same for heart disease but you know that is a specious and basically fallacious argument but I get your main point, which is, where do you choose to draw the line?
Here's a simple way to look at it: Addicting drugs really, really bad; unhealthy diet is just bad. It takes a whole lot longer to get to the end game. And with the drug addiction it's a whole lot easier to blame someone or something else for the problem instead of the "victim's" own behavior. So society looks for someone else, like government, to solve the problem.