I think that the issues I have with natural family planning methods are
1. failure rate - perhaps you might sell it better as fertility reducing measures rather than contraception?
2. alternative options and their failure rates, contraindications, risks and noncontraceptive benefits
3. the effort involved to monitor temp/cm/document and analyse the data
4. the biological increase in sexual desire at more fertile points in the cycle
Bottom line for me is that either I want to prevent a pregnancy as effectively as possible or I want to be pregnant as soon as possible. So I use contraceptive measures with the lowest failure rate until I want to be pregnant, then look for fertile signs and try the JK method.
I can see advantages of NFP but it's not for me