An overly cautious FDA?

Is the FDA acting once-bitten, twice-shy after Vioxx and Bextra were pulled off the market? Michael Fumento indicates that it may be overreacting to reports of problems with the most effective multiple sclerosis medication developed to date, Tysabri. Why? The FDA cites three deaths of Tysabri users from a virus known as PML. Read the whole article for a full explanation, but the following is most worrisome because it seems that the FDA is coming closer to implementing the odious precautionary principle:

It's possible that in suppressing the immune system's attack on the brain and spine, Tysabri may have let loose the virus. But tremendously complicating matters is that all three patients were also on other immunosuppressive drugs at the time, leaving the real possibility that Tysabri alone is harmless. There are no known cases of PML in patients using only Tysabri, according to the FDA.