One of the dangers of knee-jerk legislation is that it sometimes has unintended consequences, so what is generally a good idea can have its downsides. Anti-harassment legislation is a good example of that – as this morning’s Guardian notes, its vagueness means it’s a handy tool for firms to stop people protesting about them – and as Mr Eugenides points out today, it applies to anti-smoking legislation too.

The quick summary: banning smoking in public places is good news for health, but too draconian a ban and it’s possible that you can actually end up doing more harm than good.

Mr E links to a Scotsman story, which mentions research that’s actually been kicking around for a while.

The researchers studied data from the US, where bans have been up and running in California and New York for a number of years. The presence of the nicotine by-product cotinine was recorded to see the effects of such bans.

The results found that bans on buses, in shopping malls and in schools had the desired effect of reducing the levels of tobacco inhaled by non-smokers. But once bans were imposed in recreational places such as pubs, the results shifted markedly.

The researchers said: “We find that bans in recreational public places can perversely increase tobacco exposure of non-smokers by displacing smokers to private places where they contaminate non-smokers.”

Smoking’s less prevalent among well-off people than poorer people, so such displacement is likely to adversely affect poorer kids. As Mr E. says:

Adda and Cornaglia suggest that this may be because the prevalence of smoking is higher in poorer households; as a non-smoker, you are more likely to share your home with a smoker if you are poor. Displacing smoking from the pub to the home will therefore affect the poorest section of society disproportionately hard.

I don’t think this is particularly surprising or controversial, and it’s something that may well disappear in the long term. However, the boss of anti-smoking pressure group ASH Scotland simply discounts it and implies – libellously? – that the researchers are in the pocket of Big Tobacco. Mr E, again:

The study quite clearly supports higher taxes on cigarettes as an effective way to reduce exposure to smoke, and also supports a workplace ban. The authors were sponsored by the ESRC and there is no evidence whatever of any support from the tobacco industry.

…The researchers concluded: “Governments in many countries are under pressure to limit passive smoking. Some pressure groups can be very vocal about these issues and suggest bold and radical reform. Often, their point of view is laudable but too simplistic in the sense that they do not take into account how public policies can generate perverse incentives and effects.”

I don’t have a particular axe to grind here – as I’ve said endlessly, I’m in favour of the ban but appalled by the some of the loons behind it – but I do think it demonstrates the problems of swallowing any pressure group’s agenda wholesale – whether they’re pro or anti-smoking, pro or anti-capitalist, pro-business or pro-environment or anything else. By their very nature, single-issue pressure groups have tunnel vision and a belief in the pure, simple truth – but as Wilde wrote, the truth is rarely pure and never simple.