Hi Thoughtfulone,
Here is another angle. I don’t pretend to be an expert here, so hopefully I don’t end up spouting any heresies!
My understanding is that the opposition to ABC is due to a natural law argument. Natural law is a philosophical concept, and is tied up with the idea of Aquinas’ (and Aristotles before him) four causes. The idea is that every change involves four types of causality, one of these being what’s called “final” causality. A final cause is the end towards a certain change is directed. For instance, the final cause of an acorn is an oak tree. If something obstructs the flourishing of an acorn into an oak tree, then something has gone wrong. Without this concept of a final cause, it is very difficult to talk about things going wrong, or being bad, deficient etc.
Now, God, in his infinite wisdom has written this natural law (i.e. these final causes) into the world and any obstruction of them is a form of imperfection. Because we live in a fallen world, these imperfections abound. We can examine the workings of the world to try and deduce these final causes and therefore God’s natural law, his Will for the world.
That brings us to morality. We have two sources of moral law, the natural law and revelation. Where-ever the natural law deduced by ourselves contradicts the moral law revealed in revelation, we are to defer to the latter. For instance, from natural law, we know it is wrong to injure someone, as this impedes the final cause (or end) of a part of their body. We know it is wrong to tell a lie, because the end of our communicative faculties is to reveal what we think about this or that, and to tell a lie is to purposely not reveal what we actually think and therefore we obstruct the end of our faculties. There is a massive volume of literature about natural law, and I would refer you to that for a more complete (and no doubt more accurate) explanation.
Finally, this brings us to sexuality. It is clear that one of the natural ends of intercourse is the creation of new life. It is also clear that, by examining the effects of loving intercourse on a couple, it deepens and strengthens their relationship. Via natural law, it is objectively wrong to “mess with” either of these two ends to sexual intercourse, in the same way it is objectively wrong to injure someone because it “messes with” their normal bodily functions.
I have to stop here for the time being, but hopefully that will help a little. I can expand further regarding the natural law theory with respect to medicines etc.
May God truly and deeply bless you.