Regarding eating seconds as a self-destructive act is short-sighted. The same man can both eat seconds and not be or look "like a pig", i.e. overweight, He just needs to exercise.
That's cognitive dissonance. Self-destructive behavior is just one example of a weird way we deal with that tension (in this example, maybe that's the person who says "I have bad genetics, so it doesn't even matter anyways!" before stuffing their face).