There is a difference between wanting to live comfortably, which is rational, and actively seeking ways to exploit others for your own gain beyond what you need to live. Greed isn’t “I want to have enough”, it’s “I can never have enough”.

Society has always thrived on a measure of generosity. So many cultures have customs around giving gifts, because that’s how you build a support network of people that will help you out when you need it. Greed is shortsighted and destructive.

Or would you want to voluntarily waive parts of your salary?

Depends on the reason. If the waived amount goes to paying for healthcare, support someone suddenly unemployed or maintain infrastructure that I or other people need? Sure.