Without a certain amount of fat in your diet, the body will not operate properly. One good example is testosterone production in men. If you don't have enough fat in the diet, the body makes less testosterone, and test. is a hormone that helps reduce fat storage (provided the diet/exercise is good). Fat is also needed to keep the skin smooth and hydrated, as well as the hair and nails. It helps lubricate the body as well.
When we stop eating deep fat fried fast food and processed foods, your fat intake plummets. Even looking at my intake today, I'm sitting at a meager 25g of fat, or 15% of my calories. Because of this, I'll have a tbsp. of natty PB later tonight, or if I had some, Flaxseed oil (or a little of both).
Eating fat doesn't make you fat. Eating too many calories (fat, carbs or even protein) is what makes you fat.