No excuse for obese children. I find it inexcusable having a large amount of obese people in society. Now I'm talking about fat unhealthy people, not just big people. There are some "big" people who are fit, and strong or "solid" - however obesity is just inexcusable - though loads put excuses attributed to it, such as genetics being the favoured one as well as medical issues and so on (which is fair enough). However that's so rare it falls well outside of the standard distribution and undoubtedly less than a few % actually have a genuine issue.
It's about eating the right foods, doing some exercise, and not eating more than you expend. If you don't do that - you'll gain weight. It really is that simple. Problem is it's a vicious circle, as you get fatter your insulin sensitivity decreases and as such your body wants to store more fat etc...
A calorie is a calorie irrespective if it's sugar, carb, protein. Admittedly, the nutritious qualities of those elements are important to how you want your body to react.
Ultimately:
Calories in > Calories out = weight gain
Calories in = Calories out = weight sustainment
Calories in < Calories out = weight loss
It really is that simple. As I touched on, as you get bigger your body's hormonal profile changes, and in men certainly testosterone and the ability to store and use muscle decreases (unless you have got a decent amount of muscle mass), and as such it makes it increasingly difficulty to lose weight.
I will add... that eating the right foods and keeping insulin levels in control do help - and with modern foods being loaded with sugars and crap doesn't help - however, it doesn't change the fact that a calorie is a calorie. However, the food profile is important - for a healthy nutritious lifestyle you need to vary the diet.
However, we were not designed to be sedentary either - activity is important too! Too many people sitting in front of tv, computer games and so on.