I've found a good analogy for people, especially men, who question the whole natural birth thing is to compare it to a marathon (I know this is done to death). If you were half way through a marathon, would he be cringing because you're in pain or would he be encouraging you and supporting you? If he was doing the marathon, would he want you to undermine him by injecting him with dangerous drugs, knocking his legs out from under him etc etc? Or would he want your support to the end?

pp have given you some good sources for research. The main issues for him to understand is the effects different drugs can have on you and the baby. Rhea Dempsey's birth classes would be good for this. If he really can't support you, I recommend you having a doula. You need someone you can rely on to help you through. If he can't handle you being in pain, it becomes about what he can handle, not what you can handle.

btw - hypnobirthing or hypnobabies are good ways to learn to get through a natural birth.