Advocates of the “precautionary principle” tend to speak as if their position grew naturally out of a reasonable risk aversion. Their opponents tend to suspect that “precaution” is really a cover for technophobia and mixed with a desire to justify intrusive regulation. My own view, for what it’s worth, is that precaution really reflects a sort of Taoist preference for inaction over action. Not that motivation really matters — a principle can be a sound one even if urged for unsound reasons — but here’s what I think is a bit of evidence.
If precaution were simply an inference from risk-aversion, then one would expect its advocates to be in favor of acting, as well as abstaining, to reduce small risks of large disasters. For example, they should be arguing, if not for the immediate mass administration of smallpox vaccine, at least for the stockpiling of such vaccine in case of a bioterrorist attack and for a crash program to develop better vaccines (one more versatile against possibly resistant strains and having fewer side-effects). Yet that doesn’t seem to be the case. The precautionary principle arises out of the same “bioethics” frame of mind that opposes vaccination because it is certain to cause some deaths while the threat against which it protects is only speculative.