Thin people need this education just as much as fat people. And secondly, all currently known weight-loss techniques have been abysmal failures. No other medical recommendation has such a high failure rate. Until science has come up with a way for people to lose weight and keep it off permanently, it is useless to recommend weight loss. It may even be damaging to the public health, since there is some evidence that repeated diets can lead to binge eating and choosing much less healthy foods.
Many dieters end up regaining more weight than they lost.
Some feel that the diet craze in the last few decades is at least partly responsible for the increasing rate of obesity in America. As a society, we have chosen to join together and share in the funding of public health care. We do not get to pick who deserves what portion of the resources available. Athletes use more health care services because they are at higher risk for broken bones, injuries to soft tissues, etc. Those who drive cars put themselves at greater risk for traffic accidents.