If and only if they had that kid as spare parts and didn't love and cherish that child as all children deserve to be loved then the parents would be selfish and shouldn't have EITHER child. However, we don't know what goes on behind the media glamor screen so we are in no place to judge. I hope the second child is loved just as much as the first, and that the first is loved just as much as the second. You never truely know what motivates people any more.
I'm comfortable and quite sure of why I exist at least...I wish more people were as sure as I am ;) I suppose everything does happen for a reason...