The Catholic position on birth control is straightforward in a sense: the ends of sex in marriage are procreative and unitive, just as form and matter, and to intrinsically remove either via BC or rape, respectively, is to degrade the sacramental union by corrupting the ends for which God ordained.
Yes, well stated. Contrary to what Ialmisry implied earlier, the Fathers arraign with the greatest severity both men and women who deliberately frustrate the purpose for which the union of the spouses was ordained by God. Beside the well known example of Onan in Gen 38 cited by St. Augustine and St. Jerome, St. Clement of Alexandria's and St. Epiphanius of Salamis railing against the lawless practice of certain early sects, St. Hippolytus condemns those type of 'contraceptives' that function more as abortifacients, "they use drugs of sterility or bind themselves tightly in order to expel a fetus which has already been engendered" , St. Caesarius of Arles declares, "Who is he who cannot warn that no woman may take a potion so that she is unable to conceive or condemns in herself the nature which God willed to be fecund?" while Lactantius writes, "God gave us eyes not to see and desire pleasure, but to see acts to be performed for the needs of life; so too, the genital [’generating’] part of the body, as the name itself teaches, has been received by us for no other purpose than the generation of offspring." Several other patristic citations can be found by those interested in the link below. http://scripturecatholic.com/contraception.html
There is also a condemnation of φαρμακεία ('Pharmakeia') in the New Testament itself, usually translated "witchcraft" or "sorcery" (cf. Gal 5:20, Apoc 21:
, the context makes it more likely it refers to drugs or potions used to procure sterility (see https://www.catholicculture.org/culture/library/view.cfm?recnum=10818
for a discussion and some references). Denunciations of potions or medicines made for the same purpose as modern birth control pills are absolutely universal in the Fathers, and they present consenting to it as the most degrading of acts, St. John Chrysostom laments "Why do you sow where the field is eager to destroy the fruit, where there are medicines of sterility, where there is murder before birth? You do not even let a harlot remain only a harlot, but you make her a murderess as well ... Indeed, it is something worse than murder, and I do not know what to call it; for she does not kill what is formed but prevents its formation. What then? Do you condemn the gift of God and fight with his laws?" and presciently notes lawless couples who regularly practice it often end up viewing what is universally considered a blessing, the gift of children, as rather a curse. Something very much true of today's godless materialistic culture. "that which is sweet, and universally desirable, the having of children, they esteem grievous and unwelcome."