The proof is out there. Paul promised to openly trash me on his list if my name ever came up after we had a parting of ways, over his unprofessional gossip and personal questions. Until that experience, a few years ago, I never would have believed that protection was needed for people on a discussion list. Since that time I am very careful about the lists I join, post to and stay with. We've done that already, and I'm NOT a professional.
Quality is what needs controlling.
How can you control Quality without controlling content. I don't see how requiring accreditation of private lists will do anything to address this problem. Who is going to enforce your quality standards. But that's your business. The means by which you enforce them is another story.