I disagree: I think the argument is a load of hogwash. According to the film, the humans (obese, on barcaloungers, watching screens, etc.) got that way because "extended time in space caused their bone mass to shrink." However, even if you don't believe that little morsel, chew on this: the obese humans in the barcaloungers are zipping around their spaceship fully 700 years after the humans (of normal size, as evidenced by the videos of Fred Willard and the photos of the previous Captains on the wall of the bridge) destroyed the earth. Thus, it's conclusive that the obese people did not destroy the earth. People of average weight destroyed the earth and their descendants became obese.

I also think the people sitting on padded seats, sipping drinks and staring at a screen was a nudge aimed at...well...the moviegoers, most of whom are sitting on padded seats, sipping a drink, and staring at a screen.