“How about this: why do the good ABCs at Whatever College allow the bad XYZs to remain part of the “Greek System” at that college?”
This is an imperfect analogy here, but it’s rather like saying why does the “good” Orchestra allow the “bad” Band to be remain part of the musical extracurriculars. Or maybe why does the “good” tennis team allow the “bad” lacrosse team to be part of the athletic extracurriculars. The good ABC’s simply don’t have any power to push out the bad XYZ’s any more than the tennis team can kick out the lacrosse team.
“Why do the members of sorority DEF continue to go to parties at XYZ after bad behavior?”
That’s the one I wish I had an answer to. Some girls like bad boys. I don’t get it. I think the sororities should be more unified informally in refusing to send girls to “bad” fraternities. However, if a sorority were to try to restrict the movements of its girls, then they’d be tarred with the “see? they control your life, they tell you what to do, who to socialize with and not socialize with, conformist conformist” brush.