depends on the kind of peanuts you eat. dry roasted with extra salt...honey roasted...plain, unsalted, unroasted?
peanuts aren't bad as long as you don't load them up with salt or extra fats for roasting.
but, the ARE mostly fat, and while we do need fat in our diet, a small handful once per day is the most you should really have.
i get mine in the form of natural peanut butter, or almonds, since other nuts have better fat profiles than peanuts.