I've been looking on the other threads about NFP and I've noticed one trend that a lot of women follow when trying to defend their use of NFP/convince others: they do not want to put any "artificial hormones" in their body. This reasoning seems great in practice, but I have a few questions out there for those women who use this reasoning. 
Do you only buy and eat completely organic, hormone-free meat and other foods? Do you follow a strict vegan diet so as to not pollute your body with anything "unnatural"? Do you trust your body's natural, God-given defenses against diseases or do you get vaccinated? Do you cure your headaches and cramps with natural methods or do you use pain killers? Do you advocate the use of prescription drugs for problems like bi-polar, depression, ADD, and other disorders that are biological in nature and therefore a part of what God gave us? 
Questions like these make me wonder if the "anti-artificial" reasoning is just a way of trying to defend your religious decision in a secular world. 
Just some food for thought.