Capital is supposed to be mobile. Economic theory is based on the idea that capital should flow to its best use (e.g., investors should withdraw it from companies that aren't generating sufficient returns and provide it to those who are) including being able to flow across international borders. Labor is restricted from flowing across international boundaries by law and even job hopping within a country is frowned upon by society.
We have lower rates of taxation on capital (capital gains and dividends) than on labor income because we want to encourage investment. We're told that economic growth depends on it. But doesn't economic growth also depend on people working and shouldn't we encourage that as well?
There's an entire industry dedicated to tracking investment yields for capital and we encourage the free flow of this information "so that people can make informed investing decisions". Yet talking about salaries with co-workers is taboo for some reason.
The list goes on and on and on.