What if you didn't know you were being underpaid (say, by half)? Unless you knew that your salary was low compared to your peers, you would have no way to do #4

What if you didn't know you were being underpaid (say, by half)? Unless you knew that your salary was low compared to your peers, you would have no way to do #4 or #5 because you were blissfully unaware. What if you didn't know that all of the folks of your gender got paid 16% less than the folks on the team of the opposite gender? How would you know this and/or do something about it? It's not about being happy with your salary, it's about being treated fairly. How can you expect to be treated fairly without the data?