In all fairness, on the side of those who have a really hard time controlling their weight, I've known two people in my life that absolutely could not ever, with out drastically, and I mean drastically, changing their life styles, keep the weight off. One was a buddy in college who wasn't a super dieter, but still exercised regularly, ran and ate reasonably - better than met at least, but was always overweight. He was always a really big guy, but was never able to keep the weight off, especially after college, so he gave up and just does what he wants now. To him, 50# less isn't worth being unhappy.
Another buddy of mine is a perfect example of some one who is genetically (or what ever the cause) large. He and I graduated from college in the same class and got a job at the same place. We lived together, worked out together and some times at together. Every other week or so we'd all go out for wings or dinner or what ever, but most of the time he consumed equal or fewer calories than me, could run faster and longer than me and could outlift or perform me in almost everything. I maintained around 170# of mostly muscle (ah, those were the days!) while he was lucky if he could get down to 230#. He had a lot of muscle, and was a big-boned guy to begin with, but definitely had a lot of excess fat. Now that he's married and not working out as much, he's closer to 300#. His weight can't be explained at all as a lack of self control or physical activity; well, at least it couldn't when he and I lived together for over a year.
On the flip side, it's tough not to judge when you see a morbidly obese person (regardless of your metric, you know when you see some one who is morbidly obese) lugging a shopping cart full of meats, snacks and sodas. It's like trying to hold back your prejudice of some one with a creepy mustache wearing a trench coat and shower shoes, and is carrying around a handful of colorful entertainment dvds.
