As to #2, another answer could be that the larger, more "popular" sororities would proliferate at the expense of the smaller ones to the point that many chapters would close. Face it, we all have chapters who are at or near the bottom of their campus social ladders and some would be gone in 2 years!
Because we all have these chapters, I don't think any one NPC group is going to stand up at the national meeting and suggest that we remove quotas! Our sororities have put way too much money into their chapters, especially those with houses!
