Thalidomide
That was an unusual case (and also a very old one, which happened under much more primitive research technology than is in current use), but my point still holds. The level of scrutiny and standards of proof currently required for new drug approval delay new drugs by years -- and most of those drugs have benefits that far outweigh their incidence (if any) or serious side effects. All the people who died or suffered serious harm due to those delays need to be offset against the few who are harmed or killed by the occasional premature approval of a drug that turns out to have serious problems.
Lots of innocent people have gotten killed in Iraq since the U.S. military went in, but only loony leftists fail to offset that number against the much greater number of innocent people who were getting killed every year before we went in, and would have continued getting killed if we had stayed out.