This may just be a pessimal interpretation of humanity, but I definitely read that sort of flip response as a quick way to dismiss the entire side's merits, attempting to show that they have an obvious agenda, are ignoring something obvious that shows they're wrong, etc. I certainly could be misinterpreting.

The methedology of the original 2005 study has been questioned. To me it sounds like the researches may have conflated weight loss caused by illness with having a low BMI at time of death.

"... epidemiologists from the ACS (American Cancer Society), American Heart Association, Harvard School of Public Health, and other organizations raised specific methodologic questions about the recent Centers for Disease Control and Prevention (CDC) study and presented analyses of other data sets. The main concern ... is that it did not adequately account for weight loss from serious illnesses such as cancer and heart disease ... [and] failed to account adequately for the effect of smoking on weight ... As a result, the Flegal study underestimated the risks from obesity and overestimated the risks of leanness."

http://www.medscape.com/viewarticle/505703 http://en.wikipedia.org/wiki/Calorie_restriction