What does the Catholic Church teach about contraception and is this moral doctrine being contradicted by post-conciliar popes?
The Catholic Church has always taught that contraception is intrinsically evil. Popes Benedict XVI (in 2010) and Francis in (2016) both seem to contradict this principle. It is a good time to read again the explanatory note issued by the SSPX in 2010.
Church doctrine: an always intrinsic evil
The Church has always taught the intrinsic evil of contraception, that is, of every marital act intentionally rendered unfruitful. This teaching is to be held as definitive and irreformable. Contraception is gravely opposed to marital chastity, it is contrary to the good of the transmission of life (the procreative aspect of matrimony), and to the reciprocal self-giving of the spouses (the unitive aspect of matrimony); it harms true love and denies the sovereign role of God in the transmission of human life" (Vademecum for Confessors, 2:4, Feb. 12, 1997).
In 1968, Paul VI condemned in the most clearly way abortion, sterilization, and contraception under all its forms (condoms and other barrier methods, spermicides, coitus interruptus [withdrawal method], the Pill, and all other such methods).
[W]e must once again declare that the direct interruption of the generative process already begun, and, above all, directly willed and procured abortion, even if for therapeutic reasons, are to be absolutely excluded as licit means of regulating birth. Equally to be excluded, as the teaching authority of the Church has frequently declared, is direct sterilization, whether perpetual or temporary, whether of the man or of the woman. Similarly excluded is every action which, either in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible" (Humanae Vitae, #14).
In a well-done tract, Catholic Answers has summarized the constant and definitive doctrine of the Church on contraception. In short points with good reference, CA shows how experience, natural law, Scripture, Tradition, and the magisterium all testify to the moral evil of contraception.
Recent popes: exceptions are possible!
Although Church teaching on contraception is to be held as definitive and irreformable, recent popes in interviews have done damage to this teaching.
Pope Benedict XVI in 2010 in his book-length interview entitled Light of the World and released on November 23, 2010 declared that use of condom for a male prostitute can be “a first act of responsibility” and “a first step in the direction of a moralization”. One month after, the Congregation for the Doctrine of the Faith issued, on December 21, 2010 a "Note on the trivialization of sexuality—regarding certain interpretations of Light of the World."
The first breach was made: the pope was attempting to give some goodness to unnatural acts in a particular case.
On February 18, 2016, the Pope told journalists on a return flight to Rome from Mexico that contraception may be “the lesser of two evils” for parents wanting to avoid conceiving a child disabled by the Zika virus.
The same method of gradual morality in particular cases is now extended to the unnatural act of contraception.
SSPX: the lesser of two evils is still evil!
In 2010, the Society of St. Pius X published a note correcting Pope Benedict's words. At the time the remarks by the pope have been perceived by the media and by militant movements in favor of contraception as a “revolution”, a “turning point”, or at the very least a “break” in the constant moral teaching of the Church on the use of contraceptives.
The following extracts will apply a fortiori to the most recent statement of Pope Francis.
The fact that condom use is an intrinsically immoral action, and matter for mortal sin, is a constant point in the traditional teaching of the Church, for example in the writings of Pius XI and Pius XII, and even in the thought of Benedict XVI when he says to the journalist who is questioning him, '[The Church] of course does not regard [the condom] as a real or moral solution,' but nevertheless the pope allows it 'in certain cases'. But that is inadmissible from the perspective of the Faith. 'No reason,' Pius XI teaches in Casti Connubii, (#54), 'however grave, may be put forward by which anything intrinsically against nature may become conformable to nature and morally good.' Pius XII recalls this in his Address to Midwives (October 29, 1951): 'No ‘indication’ or necessity can turn an intrinsically immoral action into a moral and licit act.' St. Paul condemned the opinion that evil may be done so that good may come of it (see Romans 3:8).
Benedict XVI seems to consider the case of the male prostitute according to the principles of 'gradual morality' which claims to allow certain less serious crimes so as to lead delinquents progressively from extremely serious crimes to harmless behavior. These lesser crimes would not be moral, no doubt, but the fact that they are part of a path toward virtue would render them licit. Now this idea is a serious error because a lesser evil remains an evil, whatever improvement it may indicate. As Paul VI teaches in Humanae vitae, (#14), 'Though it is true that sometimes it is lawful to tolerate a lesser moral evil in order to avoid a greater evil or in order to promote a greater good, it is never lawful, even for the gravest reasons, to do evil that good may come of it (cf. Romans 3:8)—in other words, to intend directly something which of its very nature contradicts the moral order, and which must therefore be judged unworthy of man, even though the intention is to protect or promote the welfare of an individual, of a family or of society in general.'
Tolerating a lesser evil is not the same as making that evil 'legitimate', nor including it in a process of 'moralization'. Humanae vitae (no. 14) recalls that 'it is a serious error to think that a whole married life of otherwise normal relations can justify sexual intercourse which is deliberately contraceptive and so intrinsically wrong,' just as one must say that it is an error to propose the idea that a condom, which in itself is wrong, could be made right by the hoped-for path toward virtue of a male prostitute who uses it.
As opposed to a weaning process that would lead from a sin that is 'more mortal' to one that is 'less mortal', evangelical teaching clearly affirms: 'Go and now sin no more' (John 8:11) and not 'go and sin less'."