Again, only in the interests of being fair here, there is evidence that pain meds can actually make things worse (for both the mother and the child) under certain circumstances.
They can prolong labor, and because the woman can't feel what's going on "down there" as well as she would be able to without the meds, it significantly increases the chances of trauma to the vagina and perineum during the pushing stage, because the woman can't tell when to stop or how to properly regulate her exertion.
I certainly wouldn't blame a woman for taking them, but the argument could be made that it's a bit of a trade off. Pain meds might take the edge off of the immediate pain of labor, but they also increase the mother's risk for complications and a painful recovery that might be longer and more traumatic than it would have been otherwise.
Excellent point on relaxation though. I've actually heard that a small percentage of women can even orgasm during childbirth if they are able to relax enough for it.