I think you value their work too little. I worked as a realtor for a time and admittedly not a good one.
A good realtor has knowledge of current values in the local market, issues to look for throughout the transaction, which services will be needed and who can be trusted to provide those services.
There is often an element of buffering communication between buyer and seller, but it's not just a trust problem. Due to their different interests and perspectives, they will tend to communicate in ways that could offend the other party inadvertantly. A good realtor is skilled in smoothing this over and being more objective.
As an aside, the term realtor is trademarked and is something on top of real estate agent, but for the American public the realtor association has been so successful that almost every agent joins.
At the time I did this work, the requirements for licensing were indeed too lax in my state and therefore a commensurate number of lower quality agents. Which of course feeds the impression that agents are useless, because it was more true.
My understanding is that licensing the has since tightened.
None of that detracts from the fact that a good agent does quite a bit of work to build up knowledge, and to assist through a huge transaction that most people will seldom make and therefore more likely mess up.
Unfortunately this work is also often spent doing things that never lead to a transaction, such as multiple showings to buyers prior to finding a fit, or preparing listings that ultimately fail to sell for whatever reason. These costs need to be accounted for somehow, so we end up thinking only of the services rendered in our dealings.
I realize I have even more to say but I gotta stop sometime...