Realtors offer some value in knowing the market, but that's not worth a 3% commission on both sides of the sale, IMO. I already mentioned landlords. Property managers are essentially the same as landlords, except even more useless most of the time.
The only ones that offer anything of real value post-construction, IMO, are those that facilitate sales: title companies, banks, and realtors. Realtors are the worst of them, because they've enshrined their position in law in many states, and, as I mentioned, their commissions are simply way out of proportion with the value they provide in an age when home listings exist on the internet.
They have a problem of it being used as an investment, rather a job.
No one is suggesting that someone putting all the time and effort to get a building built shouldn't get paid for the time they've spent doing that. But that's where that payment stops, when they've gotten paid for the hours they spent working on that.
When housing becomes service AND monopoly, that is where the issue is. Land ownership is problematic, and profiting off of a state backed monopoly is even worse.
People of the same trade seldom meet together, even for merriment and diversion, but the conversation ends in a conspiracy against the public, or in some contrivance to raise prices.
– The Wealth of Nations, Book I, Chapter X.
They make money by monopolizing a piece of land, with the backing of the state, and then letting others use that land.
Even capitalists should be against them on the basis of a state backed monopoly alone.