NFP is not a burden on women. It is a tool to be used by the woman and MAN. NFP babies are a result of only one of two things. Poor observation (because it is very scientific), or more likely, lack of self control (but it's easier to blame NFP). Regardless of why there is a failure in the NFP process, the child is still a gift from God. I don't really care if a child was "wanted" or not. That is such a trivial matter. I didn't "want" half the food my mother put in front of me, but I am sure blessed to have received it. 

Have people forgotten what sex is?  Lets keep in mind that most statistical failures of NFP are a result of a broad definition. The medical community classifies any sex without contraceptives as NFP. When appropriately measured, NFP has an incredibly low failure rate. (equal to or better than most efficient contraceptives)