Bowler can you please post your source? From what I am aware of no one argues that in the case of the death of the mother NFP is the solution... Total abstinence is the solution, nay I would even argue that in such a case a priest could be able to intervene and say that if the science points to a 100% proof that she will die without a doubt. The other couple could deny the marital privileges to each other in such a case, it is stupid and absurd to think that at all times one can have marital relations. Divine providence ordains through something called life, when sometimes people have to abstain forceably... For example it happens ALL the time when people have to go out to work and travel, when the other person is in the hospital extremely sick etc... These things happen ALL the time, its called periodic abstinence...
I have yet to see a traditional priest ever argue for NFP as it was formulated by Bowler anti-clericalist tendencies with his Sola Denzingerite approach to all things dogmatic. This whole Pro-NFP and anti-NFP is a bunch of straw man arguments that are done with no real purpose in mind.
I have already argued this point previously in other post, unless you are in China where it will guarantee the death of your child and possibly extermination of you and your entire family. NFP is not licit to use in Western countries any health issues or anything other then that have to be dealt with responsibly by both couples. That means if you can't have marital relations, man up and carry your cross. Everyone in the world has to endure much more difficult crosses like total perpetual abstinence this of course applies to single/religious/priest. Just because their happens to be a certain moral situation where NFP as understood by most people is doable does not mean it will ever apply to you. We are talking real grievous reasons, that were never even conceivable before. Tell me where in the history of the world did you ever have state sponsored murder in such a massive scale as in China's One child policy? I will tell you, no such thing EVER. You can comparably go back to history and see the Hinduh caste system as a reference point of the first Eugenics program that was applied at such a massive scale. However, I am talking about not just death, imprisonment, guaranteed death to the child if you have more children. This will especially apply in the cities in China, and not equally apply to in the more Urban areas where there are some Chinese that have more then one child. I have personally spoken to two such families where they have 3 children and another one has 4 children, this is of course the minority. In some areas they are really draconian about this policy, but some other areas its not the same. In the Muslim part of China, when the NFP One Child government people go into the city to check "birth rates" they take him back on a body bag all the time. So in such a place it is safe, but all of these "first world" problems that people imagine up in their heads of "what hardship" is really like are a bunch of cowards and have no idea what real suffering is like. This is the ego-centric maniac individualistic narcissistic society we live in, ohhh poor me, poor me, poor me. Go out and meet some real people...
Many people think its permissible... They have never once been shown the contrary and to those folks their guilt is less, but this never eliminates the sin. However, I don't know if they truly have never thought about this issue before and I can't presume to know that. So if someone is practicing NFP, give them the benefit of the doubt, teach them the proper Church teaching. If they refuse to listen, you did your job. End of story. Its them going to hell, not you.
I don't know how much more clearly I could have said things... NFP is foreign to Catholicism, but certain historical major circuмstances could permit in a very limited circuмstance the practice, but it is NEVER because of health issues or economic hardship (alone). We are not talking economic hardship of raising a child, we are talking about imprisonment, fines, death... Yeah real serious problems here, none of the "I can't handle this anymore." St. Paul said that a woman shall be saved through child bearing, the same goes for the husband who has to love that woman and cherish her. We need real men in our society and more mother's that actually know what sacrifice means. This is the path to salvation, the narrow road as scripture says.