If I'm making less than someone else doing the same job, I don't feel that I've been hoodwinked. I negotiated a rate that I found acceptable, and so did they. Nobody was deceived.
I'm curious if you would feel the same if all products were bought and sold this way? Let's say you bought a new TV and you negotiated a price of $3. Then your friend tells you that she bought the same TV on the same day from the same store for $1k. Wouldn't you feel cheated? If so, how is that any different?