To assert that Maritain did not know what he was talking about when he said there was no significant moral difference between NFP-Periodic Conntinence and taking the pill (in the practice of responsible parenthood) is aburd. The great Bernard Haring said the same thing.
There is a difference between NFP-PC and contraception but not the dramatic immoral difference that the Church asserts makes one intrinsically evil and the other a virtue. The intentions and ends of NFP and contraceptive couples are the same: that conception is made impossible during sexual intercourse through deliberately chosen physical acts. One act is taking the pill; the other consists of two acts, namely, abstaining from sexual intercourse during fertile times by the physical acts of measuring and plotting temperture and cervical mucus to determine those days that are infertile and limiting sexual intercourse to only those times. The only end in these acts is the prevention of conception and this end is anything but proximate.
To assert that couples who practice NFP-PC are practicing the virtue of chastity-temperance while couples who practice contraception are engaging in uncontrolled sexual desire is an exaggeration in principle and human experience. What makes any act appropriate as a virtue ethics is prudence. Anyone can take virtue to an extreme such as throwing oneselve into the thickets and giving up the pain for the love of Christ or as a penance for one's sins.
What we don't need is stoic insensibility and the constant avoidance of moral dilemma that this Church teaching causes. For example, a young married woman with 3 children is told that another pregnancy will be life-threatening. She cannot take the pill or be sterilized to safe-guard her life because she is told that would be immoral. She must practice "risky" PC or celibacy. The hierarchy of values in this case is turned upside down. The prudent and most effective decision to safe-guard her life is morally irrelevant to the decision to ensure that every marital act has a procreative meaning.
The Church has never addressed this issue with any reasonable justification. Hence, to assert that contraception under all circumstances is immoral and intrinsically evil is unreasonable and in tension with fundamental human values and experience.