Fat Positive

So I was watching The Walking Dead this week, and discussed the show after viewing. It was pointed out how socially unacceptable it would be if a person were fat in the post apocalyptic society that was being depicted. They highlighted how the show cast only extras that were thinner or more fit looking. I agree that it would be taboo to be fat in this situation, as it would be indicative of a person taking more from the group than they needed. Being fat would be bad just the same way as not clearing you plate would be. 
Do you agree? Also, if it's bad to be fat in a society facing scarcity of resources, why would these reasons be negated in a society facing abundance? Is our current culture of fat positivity ignoring this aspect of consumption?