In some states, a buyer must be represented by a Realtor. If the buyer has no representation, then generally what happens is that the seller's Realtor nominally represents the buyer as well (dual agency). If you were to try to negotiate to not pay the commission, then your Realtor would probably refuse to represent the buyer, and they might not be able to close.
The requirement is almost certainly for a real estate agent licensed by the state, not a Realtor®, which is a registered trademark of a particular trade association for it's members.
Yes, you are absolutely right, and I'm aware of the trademarking of the Realtor name - that's an interesting story in its own right, and a very interesting approach to regulatory capture. I was just looking for statistics to find out how many people are licensed real estate professionals but not Realtors, but I couldn't find the number -- I'm betting not many. Since we are picking nits -- many states have a different licenses -- agents vs. brokers -- but both can be Realtors. Here's a good link for people who aren't in the know: https://www.frameworkhomeownership.org/blog/broker-vs-agent?...
This is not how contract negotiation works. In a market where housing demand is weak, it would be perfectly reasonable and possible to propose terms of sale which reduce the seller's agent fee or return it to the buyer in the form of a discount. Worth remembering in all forms of contract negotiation (buying cars, etc.) - just because they write it down doesn't mean you (the buyer) have to agree to it.
You're absolutely right that you can negotiate, but one of the consequences of regulatory capture (real estate agents must be licensed by the state, and may be required to complete a transaction) is that agents are disincentivized to negotiate on commission. Also agree that when the market is soft, you're more likely to be able to win a concession.