I would ask my priest about history. He’ll ask more powers that be, and you can get your concrete answer.
I doubt that NFP has ever been banned. Try posing these questions to the posters on the other site.
Does your church demand that a married couple should have sex if one of the people is not in the mood, sick, or needing to work out conflict first?
Is the woman or the man the sexual slave to their mate in YOUR religion?
In Catholicism, sex is a mutually self-giving and life-giving activity. The self-giving is on the part of the people, and the life-giving is from the Holy Spirit. Couples only engage in sex when they can have all participants FULLY engaged in the activity. (Man, woman, God) If a probable pregnancy means that the man or woman or both would not whole-heartedly welcome God to bring a new life, they should abstain.
Does your religion ban knowledge about reproduction, fertility, and anatomy? Catholicism encourages all married women to know their bodies and the cycles they go through. NFP is part, but not all of that. In knowing your cycle, you can gently explain to your husband why your arousal may be lower at certain times of the month. In knowing your body’s fertility cues, you can plan conception better. It’s much more than just spacing births. It’s self-knowledge.
Do you discuss your periods with your husband? Do you discuss your cervix? Do you share with him if your breasts are tender? Lots of Catholics do. When the two become one, their bodies become one. All of a sudden, his life is influenced by her body and vice versa. Catholics embrace the human body as a great gift.
Get “The Good News About Sex and Marriage” by West. There’s lots of good ammunition in there for your fight.