For me choosing unmedicated birth is partially a matter of control. When I was in labor with my first child I felt completely out of control, helpless. The hospital staff were telling me what I should do, and since I didn't know I had other options, I fearfully complied. I gave in to the epidural because I felt I had no other choice, and I couldn't handle the pain in those circumstances. I felt I had somehow failed for giving in, but I couldn't see how I could have done any differently.
The more I learned and the more support I sought, the more I was able to claim my own power and take control of my birth experiences. I feel powerful when I give birth without medication. I would rather feel everything, from the most intense pain to the unbelievable ecstasy of birth, than to be numb to the whole experience. There's nothing that compares to it, and being able to master the kind of control you have in birth is a monumental accomplishment. It's a beautiful balance of control and submission, and once you experience that you are never the same person again.
Birth has also been very faith-promoting for me, as I put my faith in God, and He is the one I trust to guide me in the process of working with my body and my baby. It's not about pain.