It's not okay to be greedy, nor is it okay to be selfish. And these ideas are responsible for much of the harm in the world.
It is okay to know what you need and advocate for your needs, to take care of yourself. But that is not being greedy or selfish. And to do it effectively means you have to be able to recognize the difference between a "need" and a "want". You also have to be capable of balancing your own needs against the needs of others.
A mindset of "greed is good" and "it's okay to be self" does not even try to understand the difference between "need" and "want" and provides ample justification for screwing over everyone else in pursuit of greedy (unneeded) wants.