The biggest issue with obesity, in my opinion, is activity level, or more precisely, matching intake to output. Ever seen the diet most professional athletes follow? The calorie counts from carbohydrates alone are often double what most people consume in a day, and that doesn't include fats or proteins. So what is the difference between an athlete and you and me? Almost exclusively it is activity level. Weight is in the end a fairly simple calculation: burn more than you eat and you lose weight, eat more than you burn and you gain. Now I know that a lot of work has been done on both sides of that equation, and there are varying factors that affect how much we burn or what impact our intake has on fat storage and such, but in the end if you move more and eat less you will be healthier and more likely to carry a healthy weight.
I think the issue with carbs or other specific types of foods, including fats, but less so proteins, is that they are not satiating, so it is so much easier to eat far more calories than you think you are, and they can also drive increased hunger. I can down easy 6-8 donuts, especially the Krispy Kreme basic glazed, and still feel hungry, and go for a big glass of chocolate milk and then eat "breakfast", but after I finish my eggs and whole wheat toast I start to feel full. I could have already had more calories in the donuts and chocolate milk before ever eating my eggs and toast. That is the problem with carbs in general, in my opinion. I mean I can down as much RC Cola as I can water at meal time, let's say, and then still eat my meal, while having added tons of extra calories that just don't register.
But again, aside from the many discussions about whether a sweet taste drives increased hunger, or the blood sugar issues of eating more carbs and such, in the end, eat more and move less and get fatter, eat less and move more and lose weight.