DB:
Again, we are just repeating ourselves.
The California Bar is was described as acting like a union in a 1981 lawsuit ruling in 1989. So while there are 20 and 30 year old complaints, that does not make it something other than a government body (and the justices actually just said they had to act like it–not that they were something else).
The NAR has acted in unfair and anti-competitive ways but you have still not made a strong case that they are a monopoly.
Like I said, most people licensed to do this work don’t belong to said trade organization.
My grandad founded one of the earliest Midwest regional boards (this was shortly after the NAR, which my family business predates, had started existing). The benefit for him then is the same as it is for me now. It creates a more integrated environment and some common standards for doing business (eg: ethics complaints are taken much more seriously by CAR and SDAR than the DRE).
The downside is obvious though. While still not a monopoly, it does have a tendency to become insular and for members to not want to do business outside their comfort zone.