Lets give them the benefit of the doubt, that we think skinny girls are attractive because socitey tells us so.  If society begins telling us fatties are attractive (and by their logic we all believe and go along with it), theres a few main scenarios I can see playing out. First, the market will take advantage by increasing the price of fattening foods due to their new demand, the fitness industry will shrink to a fraction of what it is, and the only viable farmed foods will be precursors to processed food (corn, grain, sugar cane, etc). Next, athletics of any sort will degenerate into something almost completely unwatchable.  A 450lb wide reciever being defended by a 375lb corner would be an impossibly small target for a QB to throw into, not to mention the dissolving of the tour de france, IronMan, soccer, and any other sport with more than 30 min of movement. Lastly, the inevitable factions will form.  Society will, as it always has, find a new fad.  "fat is beautiful", theyll say, but only fats with wide hips, FUPA's are out.  Now we get the same story starting over.  FUPA-bearing things will proclaim "what would be considered beautiful if society didn't tell us what was?"