Nevertheless, I couldn't help feel some sympathy for the prohibitionists after watching Newsnight, which treated the issue of decriminalisation as such a no-brainer that they decided to have a general discussion about "why don't governments just follow the evidence?" instead of discussing the arguments about drugs specifically.
Remarkably, none of the guests gave the obvious answer which is that politicians have to get re-elected and voters might want drug users prosecuted regardless of whether it reduces the prevalence of drug use. (Clare Fox did, however, argue that the logical conclusion of evidence-based policy is the abolition of democracy in favour of a technocratic elite.)
The three guests didn't disagree as much as Walk might have wanted them to. They all agreed that evidence couldn't dictate political objectives and they didn't disagree enormously on whether evidence could help politicians to discover whether their policies actually work.
The examples that Kirsty Walk used to illustrate good and bad evidence-based policy could not have been more Newsnight. The smoking ban was obviously good, the Iraq War was obviously bad. I have always been opposed to both of them, but leaving aside the fact that the SCOTH report on secondhand smoke was every bit as sexed up and politically driven as the infamous 'dodgy dossier' on Iraq's weapons capability, sincere and reasonable arguments can be made for and against both policies without resorting to the specific evidence that Newsnight implied was all important.
In the case of Iraq, interventionists could make a decent case for regime change by pointing out the indisputable fact that Saddam Hussein had used WMDs in the past, had invaded his neighbours in the past and was treating his own subjects in an appalling manner. If the Iraqi people had embraced Western troops as liberators and created a peaceful and thriving democracy, the silly claims about rockets being fired at Cyprus within 45 minutes would have been forgotten. The real question should have been whether the war was winnable and whether it would do more harm than good. This question could not easily be answered with evidence until after the fact. An additional moral question—whether it is worth sacrificing the lives of British soldiers to liberate a foreign country—cannot be answered with evidence at all.
In the case of the smoking ban, Clare Fox rightly pointed out that the epidemiological evidence on passive smoking (even if it was more robust) cannot, in itself, justify the extensive and uncompromising smoking ban in force in the UK. It could just as easily justify a notice on the door of pubs saying 'People smoke in here. If that bothers you, go elsewhere.'
Walk also used the example of seat belt legislation. It is probably no coincidence that seat belt laws and the smoking ban were cited as instances of sound evidence-based policy. They are often used as precedents for the 'public health' lobby to force people to do thing (or not do things) for their own good (some MPs predicted this slippery slope in 1979 when the seat belt law was debated). In both cases, evidence relating to one narrow aspect of life was used to trump other considerations such as property rights, self-determination and the economic prospects of the pub trade. As Clare Fox said, evidence is often used as a way of overwhelming legitimate objections that fall outside of the narrow view of campaigners.
Ben Goldacre was also on the panel and he made the reasonable point that although evidence can be distorted, the solution is to find better evidence, not dismiss evidence altogether. He would like to see something closer to randomised control trials for public policy, such as trying something out in one region and comparing the results to a 'control' region. (A personal idea: There are constant, annoying announcements on British trains urging people to remember to take their belongings with them when they leave. It would be a simple matter to turn these announcements off for a few weeks and see if there is more lost luggage as a result. If not, switch them off forever.) There is some scope for Goldacre's idea, though probably limited, but he made a comment that inadvertently highlighted how the supposedly objective use of evidence depends on some very subjective prior beliefs:
"Everybody agrees what we want to do overall is reduce the prevalence of drug use, reduce the prevalence of harmful use"
Do they? I don't and a good many people who take drugs presumably don't think so either. There are several schools of thought on drugs which I have crudely split into four basic groups:
1. The libertarian/free market position.
View: We don't care how many people take drugs and we don't necessarily care how much net harm they cause so long as individuals have access to their drugs in the least hazardous forms and the costs are internalised. We also want to remove the criminality from their sale, manufacture and transport.
Solution: Legalisation, regulation and Pigouvian taxation.
2. The public health position
View: We want to reduce the net harm associated with drug use and we would like fewer people to take drugs. We don't want people who take drugs to go to prison. Drug use is a medical issue.
Solution: Decriminalisation, needle exchanges, prescription of pharmaceutical grade drugs to addicts, treatment.
3. The status quo prohibitionist position
View: Drugs are bad, m'kay? It is right that they are illegal and it is wrong to make laws which are not enforced.
4. The über-prohibitionist position
View: Drugs are inherently harmful and harm is directly linked to prevalence. The best way to reduce prevalence is to vigorously enforce drug laws. It is hypocritical to ban drugs whilst facilitating drug use at the taxpayers' expense with needle exchanges and safe injecting rooms.
I support the first position, the mood of the times favours the second position and the law reflects the third position. The fourth position is held by Peter Hitchens.
What does this week's evidence say? It says that enforcing drug laws doesn't make much difference to whether people take drugs or not. So where does that lead us? On the face of it, it suggests that we shouldn't bother hassling drug users and we should have some form of decriminalisation. From my perspective, three cheers for that. But the people who say that it is lame to ban drugs and then turn a blind eye to drug use have a point, don't they? And the people who say that giving people free needles is rank hypocrisy also have a point.
Even if "everybody agrees" that reducing the prevalence of harmful drug use is the goal, it is far from clear that a system of decriminalisation would be better than total legalisation. Decriminalisation, in my view, is a miserable little compromise that would do nothing whatsoever to make drugs safer, would do nothing about the criminal networks that produce and supply drugs (which is where most of the harm is caused) and would do nothing to internalise the costs (because drugs would remain untaxed).
So what is the evidence on legalisation versus prohibition? Obviously there isn't any in the modern era because legalisation hasn't been tried for a hundred years. In the early decades of drug prohibition, it does seem that opiate addiction generally declined. It is also clear that alcohol consumption—and some measures of alcohol-related harm—declined during Prohibition in the USA and elsewhere. Although some legalisers dispute it, logic dictates that drug legalisation would probably result in a rise in drug consumption (if only because prices would fall and availability would increase). Legalisation would almost certainly reduce the risk to individual drug users, but a reduction in net harm, though likely, is far from certain.
From the narrow perspective of health, then, prohibitionists are not without evidence (and you can expect to hear more from 'evidence-based' prohibitionists as the anti-smoking lobby moves towards its euphemistic 'endgame'). If you ignore the impact on crime, the economy and personal freedom, all sorts of prohibitions can be justified. But this is the problem with evidence-based policy: it depends on what you're measuring and many of the most important things in life cannot be quantified on a spreadsheet.
As Churchill said, scientists should be on tap, not on top.