I have been contemplating this for a while as part of my ethical analysis of THR and related topics. Rather than wait until my views were solidified, I thought I would post a few thoughts now and request reader input (either in the comments or via email) to help advance my thinking. I will then write more later.
As others have demonstrated in very in-depth analyses, drug prohibition has huge ethical implications related to social class (by which I mean some combination of wealth, education, and connections — called socio-economic status in the jargon, but let’s not mince words). Those with the right combination of money, knowledge, and social network have been able to ignore any prohibition they wanted, from alcohol during the U.S. Prohibition Era to cocaine to marijuana. Moreover, the punishment for getting caught has always been worse for those who violated the laws in ways that were not aided by these. Similar observations apply to cigarettes these days, with those of higher social class facing much less restriction (owning private cars and houses where they face no restrictions, not having to take jobs that prohibit smoke breaks, etc., to say nothing of suffering much less from punitive taxes).
With regard to THR, my recent striking observation came when I was recently in Brussels, where snus is banned, but where I realized I would have no trouble acquiring it (for obvious reasons, I will choose to neither confirm nor deny that I did actually acquire it there). Anyone with the knowledge that acquiring snus is a good idea (as opposed to smoking) and the means to get it, then, has access to good European-style THR, while the majority of the population does not. As e-cigarettes are increasingly driven underground, the same concept applies. They are likely to become more expensive than cigarettes (after various costs, losses to confiscation, etc. are considered), and already are more expensive than black market cigarettes (which are easy to figure out how to acquire, though there is still a bit of an ethical issue there, with some of the most unfortunate in our society unlikely to get access to that discount). Canadians who want e-cigarettes, understanding why they should want them, and can afford for half of their orders to be confiscated by customs (doubling the effective price) can get them shipped in despite the ban.
Knowledge is probably most important, particularly having sufficient education and social networks to know who to believe. The average smoker in North America and many other places is unaware of the benefits of THR. Even those who might have heard the correct information a few times (probably a minority) have heard a hundred times as many anti-THR lies, and it takes a lot of knowledge to understand that certain tobacco companies and TobaccoHarmReduction.org are telling the truth and that the American Cancer Society and the U.S. government are lying.
With those opening thoughts, I would appreciate any comments.