John Paul II offered a different perspective than the '81 CTCR document on the matter in 'The Theology of the Body: Human Love in the Divine Plan':
In conformity with these landmarks in the human and Christian vision of marriage, we 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.
To justify conjugal acts made intentionally infecund, one cannot invoke as valid reasons the lesser evil, or the fact that such acts would constitute a whole together with the fecund acts already performed or to follow later, and hence would share in one and the same moral goodness. In truth, if it is sometimes licit to tolerate a lesser evil in order to avoid a greater evil or to promote a greater good, it is not licit, even for the gravest reasons, to do evil so that good may follow therefrom, that is, to make into the object of a positive act of the will something which is intrinsically disorder, and hence unworthy of the human person, even when the intention is to safeguard or promote individual, family or social well-being. Consequently it is an error to think that a conjugal act which is deliberately made infecund and so is intrinsically dishonest could be made honest and right by the ensemble of a fecund conjugal life.