Natural Family Planning (NFP)?

When I visited the Pro-life "prayer vigil" outside Central London Marie Stope clinic I was handed a glossy leaflet aimed at persuading people not to go ahead with an abortion, and suggesting that awful things were likely to happen to those that did go ahead. I looked up one of the website referred to in the brochure (http://www.flionline.org/) Family Life International (FLI) describes itself as a "Catholic Pro-Life/Pro-Family non-profit making, world-wide organisation".

I was struck by the piece on "Natural Family Planning" (NFP).  It seems that any form of artificial contraception is wrong, but "natural" contraception is ok, and advice is given on how the husband and wife can help each other to confirm when the wife is and is not fertile.  The piece ends with the sentence: "SAFE's design encourages the involvement and participation of a husband in the charting of his wife's menstrual cycle, thereby allowing him to be aware of his wife's fertility."

I just can't get my head around the double standard here.  It seems to be saying that it's ok after all to have sex just because you enjoy it, as long as you use the 'natural' method.  Surely if contraception is viewed as wrong it really should not make any difference what method is used.  Am I missing something?