Another thought just occurred to me…I wonder how many people even realize that the meaning of rape has gone through some dramatic changes in recent history. From biblical times up until the modern era, rape referred to the abduction and seduction of a woman still under the authority of her father. In other words, any young, unmarried woman who was seduced OR forcibly violated was raped. In today’s parlance, we might call it statutory rape, but that doesn’t even cover all the possible scenarios meant by rape. A woman under the authority and protection of her father was thought to lack the ability to give free consent to sexual activity. Therefore, it was all rape. Her own culpability only came into question if the rape occurred in a very public location and without threat of violence she decided not to scream for help or fight or run. I think this is mainly because virgins were expected to highly value their chastity and virginity (obviously, right?).
So, even in situations where the girl decided to go along with sexual contact, it was still considered rape, and did injury not only to the girl (her chances at marriage) but also her family (reputation). In those possibly “consensual” scenarios (even though true consent was considered to be lacking), Aquinas would have been quite right to say that contraception would be wrong. Also, remember that the OT (Old Covenant) stated that a rapist may redeem his victim by marrying her!

When I read this as a young girl, I was absolutely horrified. The OT is definitely not age-appropriate reading for young girls, because women were treated as property, and rape was viewed more as a form of theft against the girl’s father than violence against the girl.
Aquinas was likely expounding upon these views espoused in the OT. Also, remember that he stated that ensoulment happens at 40 days for boys and 80 days for girls. Aquinas knew absolutely nothing about genetic material. Modern contraceptive technologies are BASED UPON extensive knowledge of genetic material and fertility. The Church has spoken out loud and clear about the proper context for sexuality, She has redefined rape differently than the ancient understanding of it, She has admitted there are licit uses for oral contraceptive medications, but through it all, She has been shouting from the rooftops that sexual relations are for a validly married husband and wife and that each and every marital act must be unitive and procreative. She has had to be ever more clear about this as the centuries passed, because as human understanding of the natural world has grown, so too has our hubris. She had to take up new terminology, but use them carefully with clarifications, because older terminology doesn’t acknowledge all that we now know about human sexuality, genetics, procreation, etc.
Aquinas might have said contraception even in rape was wrong…I don’t see that specifically said in the documents given here, but in case I missed it, let’s explore that a bit.
Would a saint really have said that repelling a rapist so that he must withdraw prior to ejaculation is wrong?
Would a saint really have said that a virtuous young lady must remain passive during a rape because it is the nature of the venereal act to beget children?
Would a saint really have said she may not cleanse the semen from her private parts after the attack?
I seriously doubt he ever would have meant to imply any of those things. And the fact remains, that our knowledge has grown, and our technology has grown. Aquinas did not know about aggressive little cells called sperm. Aquinas did not know about ovulation. Many of the so-called contraceptive techniques used in the ancient and medieval eras were only possible in consensual sexual behaviors or were actually abortifacient potions and suppositories. These of course would be rejected by him, as well they should by us today.