If we learned anything from the recent experiment with "legal highs" it is that the law does make a difference. The idea that prohibition has little or no effect on drug use beyond criminalising users turned out to be wrong.
A few months after synthetic cannabis was legalised last year, something strange happened. We started hearing and reading about the distress it was causing to users and their families.
This was strange because these products had been in the country for years before the law caught up with them and in all that time we had heard or read hardly anything about their damage. Why?
This was a question Associate Health Minister Peter Dunne was asking publicly during the furore over the relatively few products given interim legality while his officials worked out a way of testing the safety of psychoactive substances.
He never got an answer at the time and I haven't seen one in the four weeks since Parliament passed urgent legislation cancelling the interim permits. The most likely answers are usually the most obvious.
It may be that legalising a drug increases its use. This should be obvious but it has been obscured by the old credo that drug users are indifferent to legal risk and just as many users were around when they had to get their supplies underground. Unlikely, when you think about it.
Or it might just be that legalising a drug allows people to talk about it publicly. This is interesting in the case of legal highs because they were not actually illegal previously. Yet the anguish was not on television.
It suggests that when Parliament passes a law it is doing far more than regulating an activity. To the extent that it is sanctioned, the activity is seen to be approved and those who gave it approval become responsible for its problems.
That means those suffering the problems can blame politicians for them much more effectively than they could when the substance was in a legal limbo. So they come forward in their quivering teenage wreckage and distraught motherhood.
Whatever the reason, the law makes a difference. We are not going to see cannabis legalised for as long as politicians remember the lessons of 2014.
But there is another inhaled substance that could pose a similar problem. What should the law say about these "e-cigarettes"?
They are little tubular batteries that deliver a vapour containing nicotine without the tar and other carcinogens in burned tobacco. Isn't that thoroughly good news?
People can be free to enjoy all the social pleasures of smoking without the risk of cancer - or they could if the devices delivering the drug without the gunk were permitted in New Zealand.
As yet, e-cigarettes containing nicotine are not approved for sale here although last week the Herald on Sunday found five Auckland outlets selling them with the drug in a separate cartridge.
They seem to be in the same limbo that "legal highs" used to be, while the Ministry of Health wonders what to do about them.
One of this country's most prominent anti-smoking campaigners, Dr Murray Laugeson, wants them approved as a means of helping addicted smokers to quit. In this they have proven effective though the Economist observed last week, it depends how you define "quit".
E-cigarettes are a means of quitting tobacco, not nicotine, their drug of choice. That is the reason Ash opposes them and the ministry may not approve them. But, really, can we ban a drug on that basis?
There are many drugs of choice sold lawfully with an age restriction. If nicotine is worse than any of them, we are not hearing that it is. The reason for opposition to an alternative to tobacco is that the alternative might encourage some to take up, or revert to, tobacco.
Is that a sufficient justification for a ban on something that may not do much harm in itself?
Most of us will hope it is sufficient reason because the idea of people around us breathing a vapour into the air is too much like smoking for comfort. If the stuff is coloured or, as the Herald on Sunday reported, flavoured, it is going to be unwelcome.
But can we really justify that? If the vapour is visible and harmless it is no worse than breathing the same air. E-cigarettes might tell us whether our opposition to smoking has really been about health - or something else.
Like campaigns against (beer) drinking and fast food, and cannabis for that matter, there is a certain social sniffiness underlying the health righteousness.
These things typecast people. When someone who was taken to be a non-smoker lights one up, people are quite thrown. You can see estimates being revised. I'd prefer a law against e-cigarettes too. But I can't justify it.