It is not the baby's fault that its parent's don't marry. Why on Earth would you use that word to describe the baby. Yes, we all know the technical definition. But you're using it to be cruel. TIMES ARE DIFFERENT, like it or not.
I was not the one who originally used it. I used it to make a point - better to be a bastard than murdered - to point out the absurdity of calling the child that.
I happen to have a "bastard" child.