I hope you recognize, that the statement that everyone is always paid fairly is false. Thinking otherwise borders on some kind of serious ethical blindness.
Where did they make that statement? All I'm hearing GP say is if the only way to know your worth to the market is to test it. There is no other way to measure what your employment is worth.
It was phrased that way above, read carefully. If all they meant was "if you aren't paid fairly, leave and find a better place", that's OK, but that's not how it was phrased (which was quite improper).
If you can't get more, you're not being exploited. You're taking advantage of the best option available to you.