By Peter Williams
How does that old saying go again?
Those who do not learn the lessons of history are bound to repeat them.
And one of history's great lessons is that if a product is banned, an industry emerges to sell it on the underground, unregulated and criminal market.
Prohibition in the US between 1920 and 1933 was a disaster. Gangs took over the booze industry. Al Capone and Bugsy Malone may have been romanticised in the movies but the era was lawless and out of control.
Sanity prevailed and alcohol was back, legally, for Christmas in 1933.
Things were never quite as violent in New Zealand because we rejected prohibition twice (although only just) in the referenda of 1919.
All this is relevant because on this day last year we first heard how the Green Party, as part of its deal to support Labour, won the promise of a referendum on the legalisation of cannabis for personal use.
It's easy to understand why. Cannabis is an illegal drug which has become so mainstream that police have more or less given up trying to control it. Like the old amateur rugby administrators raging against the encroaching professionalism up till 1996, the fight just isn't worth it.
Medicinal cannabis is well on the way to being produced on an industrial scale. Legalised recreational use should follow.
The governments of western nations launched a "war on drugs" in the 1960s. It was a futile contest which could never be won, just as Prohibition failed so spectacularly.
Half a century later that war is well lost. It's time for governments to start negotiating peace treaties.
This past Wednesday, Canada became the second country, after Uruguay, to legalise the sale of recreational cannabis. It will be regulated. All marijuana will be tracked from seed to sale. The most any individual can buy is 30 grams and is allowed only four plants at home.
In Canada's federal system, the various provinces will decide where the weed is sold. In Alberta, there'll be privately owned shops. In Quebec, all the outlets will be government owned.
There'll be regulations about where you can use it, how old you have to be (either 18 or 19) and how much provincial sales tax is put on top of the federal government's 10 per cent excise.
In other words, it will be like the alcohol industry. It's not perfect and people will still wreck themselves by getting high. But the price and convenience of buying at your neighbourhood store will be lower and safer than purchasing at the local tinny house.
The considerable taxes which will be collected can then be targeted for drug education.
Along with the rest of the world, we will watch closely what happens in Canada. In about a year, let's see what impact legalised cannabis use has had on public health, crime, road safety and the black market.
If the history of the post Prohibition era in the US is anything to go by, the criminal activity associated with selling cannabis will quickly shut down.
In the meantime, our politicians would do well to start thinking hard about a recreational cannabis policy for this country. What age should it be allowed from? In what form? Who can sell it? What potency can it be? Where can it be smoked or eaten?
Then the question in a referendum sometime early in 2020 (and it shouldn't be part of the election later that year because of the massive distraction that would cause) can be relatively straightforward, something like:
Should the sale, possession and use of cannabis, subject to government regulation and licensing, be allowed for persons (insert age) and over?
I'm an avowed non-user. Like the 10-year-old with the cigarette behind the bike sheds, I've taken either three or four puffs of cannabis in my life. I couldn't see the point.
But an unregulated, criminal market now involving synthetics, has led to the tangle we have today. Control the supply chain and the bad guy goes out of business.
Collect the taxes and spend the money telling us how bad the stuff is for our brain, our skin and our lungs.
Jacinda Arden says it will be a non-binding referendum but polls suggest about two-thirds of voters will say yes. Only a brave politician rejects a result like that.
But like what happened after Prohibition, the world will not be any worse off with legalised dope.