My husband is Catholic and we had to go to his church for pre-marriage counseling, even though we were to be married in my church with my preacher. A couple tried to explain the taboo on contraception to us, but it was like the game Six Degrees of Separation. You know, everything is related to the next but yet the first thing has nothing to do with the last. Anyway, they told me that NFP was okay, and I asked what the difference was between NFP and contraception. They could not answer. To me, abstaining from sex during fertile periods is birth control.
Here's the difference. Birth control is not just abstaining from sex. It is making a conscious choice to have the pleasure of sex but then to deliberately make it artificially infertile.
It is the same difference as dieting vs. bulimia. With dieting, you just practice a little self-restraint. With bulimia, you are seeking the pleasure of eating in an illicit way.
It might interest you to know that virtually every Christian denomination before about 1930 taught the immorality of birth control.