I can imagine a number of reasons why a meth habit is stupid and destructive on the individual level, but how is it a moral issue except socially? And how does that differ from other instances in which others, or one's socially instilled principles, define your obligation to others or their institutions? I doubt whether people who indulge in dangerous drugs are doing it simply as a gesture of defiance. They seek fun, and foolishly disregard the consequence. But how does this morally differ from indulging in something that is fun, simply because it's fun, which has no such consequence?
I might see drug addiction as having a moral dimension, insofar as it involves the imposition on others, the betrayal of loved ones, and all sorts of social consequences that offend my sense of what's right and good. But at the fundamental or definitional level, how does that differ from so-called moral rules that I regard as nonsense, such as endangerment of my immortal soul, or defiance of divine fiat?
theprestige has, I think, painted himself into a corner, by stating that moral principle is exclusively individual, but then seeming to deny that it's even possible to separate that from the ideas and implications imposed by others.
If we count the social consequence of illegal behavior as a moral issue, the result is that any despotic power can declare a law, no matter how crazy, and obedience to that law becomes a moral offense simply because of the social consequence of disobeying it.
I see a hint of resemblance here to Kant's categorical imperative, and what I see as the main problem with it. Kant's idealism has much to recommend it, and like so many idealistic constructs, one can look at them as a goal on the horizon, a thing you should be aiming toward. We can try to define what is good and why it's good. But at the practical level, if it's never permissible to violate a stated moral principle, then when two moral principles conflict, no action can be right. And in the real world this happens all the time. We face not a simplistic list of goods and bads, but a constant and chaotic stew of conflicts and connections and alloys. The world is complex and confusing, run not by gods but by people, many of whom are fools, fanatics, or worse. We can say that obedience to the law has a moral component, but only in the imagination of theologians is the law written in the sky by God. Down here on earth, absolutes are very thin on the ground.