Because when Panhellenic starts saying "you may not do x, y, or z during a rush party" they do not know what groups may have in their policies or in their rituals (for some groups, pref party is standardized and part of ritual). When you start prohibiting behaviors, it's a very slippery slope.
Panhellenic is doing all they can and should do.
__________________
It is all 33girl's fault. ~DrPhil
Threaded Mode
