I've been having a small debate with myself over this. On the one hand, I think having a fat girl in your friend group could help to make the rest of the group more attractive by comparison. On the other hand, letting fat girls into your friend group is like letting retards into your university: it drags down the whole such that guys will sub-consciously put an upper-limit on your attractiveness in much the same way that when we hear somebody attends a bad university, we automatically think they can't be that smart.
NS, what do you think?