Relevant to the renewed push for the misguided "Precautionary Principle", this jaw-dropping assertion (PDF) from a group of law professors affiliated with the Center for Progressive Reform, expressing concerns over the Cass Sunstein nomination:

It is difficult to think of a single public health or environmental threat that with the benefit of additional research has not proven even more dangerous over time.

David Bernstein @ Volokh doesn't find it difficult to think of such instances at all:

Mercury in vaccines; Bendectin; Silicone breast implants (and medical grade silicone in general); PCBs; Asbestos in buildings; Fluoride in water; Birth control pills; Occasional marijuana use; High fat diets; Exposure to low level nuclear radiation; New carpet fumes; "Toxic waste dumps"/Superfund sites; Moderate overweightedness; Moderate alcohol consumption; Spermicides; Metal fillings (for teeth); Cancer from physical trauma; Masturbation; Predictions in the 1970s of worldwide food shortages; "Overpopulation"; Global Warming (the predictions of the level of man-made warming have decreased dramatically, even among strong advocates of the theory); Miscarriage from video display monitors; Cancer from electromagnetic field radiation; Radon; Dioxin; Pesticides commonly used on fruits and vegetables causing cancer to "eaters";

The authors of the Center for Progressive Reform declaration, for the record, are: John S. Applegate, Indiana Maurer (Bloomington); Robert Glicksman, Kansas; Thomas McGarity, Texas; Sidney Shapiro, Wake Forest; Amy Sinden, Temple (Beasley); Rena Steinzor, Maryland; Robert Verchick, Loyola New Orleans; and James Goodwin, Center for Progressive Reform.