This poster art is obviously directed at the prevailing portrayal of the overweight woman as not being beautiful. It is not a universal notion, however it is obvious that where physical appearance is concerned, the general attitude among post-pubescent males is that the obesity retards a woman's perceived beauty.
I personally believe that two factors trump the believed influence of "society": 1) personal history and the modeling within the family, and 2) the distortion of physical cues for fecundity brought about by the body's accumulation of fatty tissue.
As regards 2), the accentuation of the baby-making compartments of the female body which naturally happens when a woman is at what is considered a healthful weight, cues the male of the species to the potential for successful reproduction. In the obese woman, these visual cues are distorted and muddled.
I think that media that exploits these natural proclivities reflects rather than creates the attitudes. All the Big Beautiful Women propagandizing in the world is not going to change this strongly inculcated, possibly instinctual, sexual psychology.
Courtesy of A 1000 Broken Dreams