Precaution and Principal...

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. - Guy Hurbert, Samisdata

Guy is responding to this piece in the London Times

Suppose that, in return for an annual premium of L1, someone promises to pay you L1 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 L1 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.

Think about that for a bit in light of what you are hearing from Truthers, Greens, and Barking Moonbats....

Sea Levels may reach 20' higher than they are now - don't take a chance, subsume yourself to the gerbil worming mantra.
Scores of Millions of Americans may die horribly, don't take a chance - we must embrace socialized medicine
You may be murdered in your bed, don't take a chance - we must melt all guns into limos for the political class
You may burn in Hell for all eternity, don't take the chance, send $50 bucks to Reverand Swaggart right now.

...it's worked in the past with predictable results.

People may die if we continue to use DDT - don't take the chance, ban it.  We banned it and 50 Million people died of Malaria.  No-one died of DDT poisoning.