Yeah, that obviously works for a small number of people. I'm talking about the large scale demographic changes though - they're clearly the result of changes in food availability in one's environment. In an environment like that seen in most of America, the majority of people are going to be fat. You don't solve that problem by emphasizing personal responsibility, even if it can in theory work for some individuals.
or c) are disciplined enough to count their calories and stopping when they hit 2,000 kCal/day or so.