Most employers will tell you not to discuss earnings. I think part of the problem is that the focus becomes on the money. Instead of teamwork and cooperation, we become jealous, and cutthroat.
When we find out that someone who we think is equal to us earns more money than we do, we get upset. We don't always see the work they have done to earn the greater amount. Maybe they got lucky with a hub topic, but when we focus on our own earnings, we are more likely to do better.
Plus, if you are making pennies, and find someone who is making thousands, even though they have millions of hubs and years of experience into it, we might get disillusioned that we aren't getting to the thousands faster.