Could have fooled me - I eat a very high-carb (but low fat and vegetarian (mostly vegan actually)) diet and am in great health and don't have any excess weight. I eat a ton of sugar too, but in the naturally-occuring form (I eat more fruit than anything else), nothing refined. I don't eat a lot of grains but do include some (I just frankly don't like them very much), and don't go out of my way to avoid fats either although I would imagine I have a relatively low amount overall. The only thing I do strictly avoid is meat and while I'll have dairy on occasion, it isn't a daily thing.
I've tried LOTS of different diets including paleo in the past, and stuck with what actually works and I feel content with. There is a reason that paleo will lead to weight loss, but there's also a probably a reason you don't stick with it consistently. Food for thought (pun intended). There are certainly lessons to be learned from it, but my main objection is that it's called "paleo" when in fact it's based on speculation (and to a degree, modern rather than actual fact and many of the things that are advertised as "paleo" foods are so far removed from what paleolithic man would have had available it's ridiculous. Of course I also find things like veggie burgers and fake meats and the plethora of refined soy products on the market ridiculous as well.
Anyways not trying to argue just pointing out that I don't think we can point at one or two specific aspects as "the enemy", and lifestyle makes a great deal of impact as well. I reckon the most important thing dietarily is to eat real wholesome foods, and not worry too much about the details of "fats", "carbs", "sugars", etc. (each of which encompasses a rather broad range of things).
Indeed! The entire digestive tract in particular is perfectly balanced over your hips better than any backpack.