FWIW I used to weigh in at over 300lbs, so I know first hand how hard it is to loose the weight. Or rather, keep it off. Like most people I ate less, to the point of starvation and the end result would be lower metabolism and the minute you go off the starvation diet you put it all back on in short order. I dont know why or what finally clicked but I just said one day I had enough and did it. Through books, the internet and the people at the gym I learned about nutrition and exercise and took the weight off and kept it off for nearly 4 years now. And I find now that I have been this weight for a while its easier to stay here "yea metabolism"

I have a couple friends overweight, and IMO it boiles down to 2 things. Laziness and lack of knowledge about nutrition.
Some people its pure laziness, TV dinners, chips, coke...Im too lazy to make something healty. "I dont buy the no time argument, its doesnt take any more time to eat an apple than scarf down a bag of doritos. You can throw a chicken breast and potato in the oven and it cooks just the same as MCain French fries and chicken nuggets".
Then theres the people who dont really understand how to eat properly. They start eating rice cakes and tofu in minuscule quantities ,join weight watchers and drop the weight too rapidly "read muscle tissue loss" and the minute they cave in because they cant stand it anymore they balloon back up because they lowered thier metabolism. Or they dont understand moderation. "Milk is good for you, what the hell are you talking about?" Milk is good for you, as long as its not 2L of chocolate milk a day. Eggs are good for you too, as long as you dont fry them in the greese from the half pound of bacon you just cooked to go with it.
Not sure what to do about it though, we let people smoke ,and thats probably just as big a health risk, and drain on the system as fat people. How do you legislate someones weight?