OP isn't saying peanuts are a poor source of nutrition. OP is saying a few peanuts are calorically dense and it is easy to consume hundreds of calories through seemingly inconsequential amounts of snacks and drinks.

Depends on what your entire diet is. If you are eating only peanuts - or anything else - that is bad. If you eat a handful of peanuts once in a while that is fine. Even a cookie every few weeks is fine, but 6 cookies a day every day would be bad. Someplace in between is generally a good place to be.

I'm assuming of course that you are "normal". If you are allergic to peanuts they are of course worse than a cookie. If you are diabetic cookies are bad.

A handful of peanuts is roughly the amount of excess calories burned in a 30 minute cardio workout (I'm assuming).