"Personal gain" is where the logic fails. I have nothing to personally gain by leaving TECSHARE a negative rating (he has purchased goods from me in the past!), nor do I have anything to personally gain by leaving negative ratings for socks and scammers. In fact, leaving negative ratings leaves one open to rating retaliation -- as has happened to me. I don't do it for kicks, and I don't do it to further my own dealings; this is why I take offence to the statement.
I think BadBear's point is that you can't defend your original feedback on the basis of a feedback he left you afterwards. There's no forward causality.