The ever-reliable Jamie Whyte has a superb piece in The Times in which he identifies quite precisely what’s wrong with ‘the precautionary principle':
Suppose that, in return for an annual premium of £1, someone promises to pay you £1 million if you are abducted by aliens (such insurance exists). … You lack the information required to know if the insurance is a good deal. It is in such situations of uncertainty that the precautionary principle is supposed to apply. … [T]his principle tells you to buy the ticket. You should incur the £1 cost of the premium if there is any chance that it will save you from the greater cost of experiencing an uncompensated alien abduction. Whenever the prize is greater than the bet, and you do not know the odds, the principle says you should gamble. Bookmakers must dream of the day when punters bring such wisdom to the racetrack.
That’s a very illuminating parallel. What those who preach precaution are doing is secretly evaluating the likelihood of the Very Bad Thing we are supposed to be scared of as certainty, and their avoidance policy as perfect.
I would add, now Whyte has given me the right analytical start, that the way that the problem is usually posed should give this away directly. The precaution preacher says that: the Very Bad Thing (B) may be unlikely, but it is so very very bad, that however unlikely it is, it is too horrible to contemplate not doing onerous things P prevent it. It might as well be certain, but for P. That is implicitly a claim that both B is infinite in horribleness and that P is guaranteed to reduce its (unknown) likelihood.
Not only is it a bad bet, but the claim to the efficacy of P should be treated with skepticism. As well to remember that when dealing with Greens, securocrats and panic-mongers of all kinds.