Why HR or a manager would have to justify what they pay someone else, I just don't know.

If someone came to me and asked why does Joe make more than me? I'd say get the **ck back to work and ask me when you are worth as much as Joe.

The audacity of even asking is beyond me. Why can't people be responsible for making their own deals and accepting it? You signed a contract, you negotiated a role and salary. If it isn't good enough for you, some years down the road, do it again or do it with another employer.