To get back to the original question, the only problem with fat is the calories. I know this sounds like a trite and silly statement but it really isn't. We all know that the problem with carbs has nothing to do with the calories but with the complex interplay of hormones, especially insulin. Protein also has hormonal effects, including effects on insulin, although it is different and not nearly as deleterious.

From everything I have read, good fats have no such effects. They don't prevent the body from burning fat. They don't blunt your brains satiety signals. They simply supply calories. Eating too much fat won't damage your metabolism or your heart. According to GaryTaubes and others, your body will simply use the extra calories. You'll do more, have more energy, raise your body temperature, strengthen your immune system or maybe just fidget more. The body has many ingenious ways of maintaining equilibrium when its not being poisoned.

However, if you want fat loss and not simply equilibrium, then the calories matter. Many people spontaneously lose weight with low carbs because of water loss and increased satiety. However, at some point, the body finds equilibrium and weight loss stops. This has to be true, otherwise it would be impossible to maintain weight on a very low carb diet. We KNOW we can maintain weight this way. So a decision has to be made. If you want to keep loosing fat, at some point, a deficit must be created and that means limiting some source of calories. If you can't (or don'w want to) limit carbs or protein further, then you have to limit fat.