It's natural - not because of cultural issues, not for hormonal reasons, not because of TV, and other media pressures. It goes further than that - back to creation. I was created (not just biologically, but put together and planned for childbirth). It was a command of God. And having been made in His Image it's only natural that I would want to have something in my image as well - a baby.
And sin ruined it all. It makes me angry that because of sin, I don't get what I want - what I was made for. Is this righteous anger?