I think the claim is that demanding what is rightfully yours is greedy and selfish. I don't know whether I agree in this case (probably not), but there have been cases in my life where I do agree.
It's that "rightfully yours" bit that really bothers me. Where does that come from and why is it so obviously rightfully yours? It takes some gumption to assume you're in the right. This land is rightfully mine because I bought it from someone else who genocided a people, but okay great, it's rightfully mine, I feel super great about it.