This post by David Zaruk at the Risk-Monger blog gives a number of examples illustrating that precaution isn't always the best strategy. Sometimes the precautionary principle is invoked as a reason to avoid taking an action. In other instances it is invoked as a reason to take an action. "We've got to do something" in the face of some problem, and "trying something" in the face of uncertainty is the taken as more cautious than doing nothing. David writes:
He goes on to point out the unintended effects of modern day precautionary actions. These typically come about because of a failure to think on the margin and to consider behavioral response. If pesticide X is banned, that doesn't mean farmers use no pesticide. They switch to pesticide Y. Thus, the better question is how X compares to Y. Another questions rarely asked: if X is banned, then what new mix crops will farmers grow instead, and what environmental, health, or fiscal effects will that have?
(Note: I don't necessarily agree with all the hyperbole in the piece, particularly the last sentence)