What makes parenthood so infinitely worthwhile? Is it worth it? Why?

I've talked to parents who say that... well, what it comes down to is that you can make a list of all the costs and sacrifices that go along with being a parent, compared to the rewards, and on paper it looks like you've come off worse for it... and yet, if you look below the paper, and at the real truth of it - the rewards are infinitely greater than the costs. I don't have kids - I don't want kids. I suspect that my particularly bad childhood has destroyed in me whatever it is that makes most people want kids.

So my question is: can you put into words what it is that makes parenthood so infinitely worthwhile?