I’m not entirely sure why this matters so much. Maybe the specifics of Catholic teaching changed as we learned more and more about the development of the child, but the idea of the sanctity of life remains, right?
Maybe I’m missing something...?
The claim of the RCC is they've always opposed abortion. But that comes down to how you define abortion and when life begins.
Roman Catholics would have us believe they've always opposed abortion from conception...as that is the their modern position after V2. However, history shows that is not the case.
I argue that Rome's position on this issue...and others...has changed. And this from the church that claims they've never changed and have been doing things the same way the Apostles did.
That just is not the case and negates the RCC position on "Sacred Tradition" being equal to Scripture.
Thomas' opposition to the Immaculate Conception should be the Roman's first clue their equating "Tradition" to be equal to Scripture to be in error. Yet they persist with this.
Scripture does not change....but Roman Catholic theology does.
The Catholic Church has always taught that abortion is a sin. The only way philosophical inquiries about embryology would make any difference, would be if there were a scientific dispute about whether they were dealing with a living human embryo, or not.
In terms of historic Christianity, the resolution of the embryological question did not make a moral difference, inasmuch as even if it were "just" contraception, it would still be a sin, intrinsically wrong, and forbidden.
Many (but not all) Protestants will still dispute about this, since, for instance, some think that the hormonal Pill is OK because it "only" blocks ovulation or it "only" blocks fertilization; whereas the Catholic (historic Christian) understanding is that direct sabotage of the transmission of life is morally objectionable, whether it occurs before, during, or after fertilization.