The other agent won't bring clients to you if the cut is too low.

This was part of the evidence used in the case. They had recordings from buyer's agents who called about non-MLS homes. The agents were on-tape saying things like, "I am going to make sure no other agent shows your house." All because the seller refused to pay a buyer's agent commission.

This is very true. A home I purchased recently, the sellers had a very new realtor, who was friends with them. She had listed the commissions very low - probably thinking she was doing them a service.

I purchased the home without a realtor, and one of the ways I had a much stronger position was because no one else was being shown the property. (As in, realtors weren’t mentioning it to their clients).

I had a friend of mine who is known locally in the area as one of the best realtors look at the mls and listing, and that was the take I got from him.

Yep. It's basically a cartel. You can do whatever you want technically. But you instantly lose the the market reach if you don't pay your realtor tax.

Plenty do. I and many friends do RE transactions with agents who are not “realtors”

That's all good and possible but not quite mainstream yet.