I know I'm going to get jacked up for saying this, but this is sort of why it's good to have the NPC expansion process. The entire panhellenic votes on the issue, and it gives the chapters a voice to air the fears of diluting house sizes and hurting smaller chapters. BUT, if it's one group holding a campus back from expanding because they aren't doing their share to help themselves, then you have to wonder if that group should even be there in the first place.
NPC expansion, while a long and sometimes arduous process, often times works. It's why DeltaSigStan's campus has 9 sororities of relatively equal size. Add 5 more sororities to match the number of fraternities, and it wouldn't be so even. Greek Life shouldn't be a survival of the fittest, but a community helping each other grow. I know that's a fantasy land, but it is nice to consider