Maybe its just me, but your post sounds awfully critical of people who struggle to stick to a diet. Most people who have yo-yo dieted or struggled to stick to diet after diet, lost weight and then piled it all (and more) back on usually have serious self esteem issues and a psychological or emotional attachment to food. The reason they can't stick to a diet or 'fall off the wagon' is because the reason they eat and are over-weight in the first place usually isn't addressed or even if it is addressed it isn't fully dealt with.
For a lot of over-weight people, food isn't just something to use as fuel, its a comfort, a friend, an addiction.
Both myself and my councellor have likened it to being an alcoholic - you wouldn't say to an alcoholic you can have a shot of whiskey three times a day but thats it. The same applies to someone with an emotional attachment to food or a food addiction, you have to eat a limited amount of food and then stop which for a lor of people is just too hard. And then when we fall off the diet we feel like failures, losers, worthless, so we eat more to compensate for our feelings and hence we put the weight (and then some back on)
Maybe my reaction is a little overboard but methinks a little more understanding and a little less judgement is required. xx