The post above is not saying that realtors are evil or useless, just that the standard commission schema means that a realtor's payoffs/incentives are quite different than the owner who hires the realtor.
The problem with having different incentives is when one party doesn't recognize that there is a mis-alignment. If you're selling your home and you don't realize that your Realtor's time is not an endless, worthless resource at your disposal, then you may be inclined to insist on your Realtor spending endless hours of aggressive negotiation, potentially putting the offer at risk of closing at all, for an amount of additional money to you that's not really going to make much of a difference to you. (My wife's been involved in deals where one party or the other has risked a deal that's been in the works for 2-3 months over less than 0.1% of the house's value.)
Admittedly, not spending 2-3 months to work out another deal is worth quite a lot of money as well. But this behaviour doesn't seem obviously irrational.
For a half-million dollar home, which would be a relatively nice house for most of the country, you're talking about $500. For any party on that transaction (buyer, seller or their respective agents who each stand to make $15k on a normal 3% commission), that's not a lot of money and is almost certainly not worth arguing over if you're in all but the earliest stages of negotiation.