I think you will have a fundamental problem of convincing people who don’t believe in soul-at-conception that abortion is always wrong.
That’s why I have studied the abortion issue from much more than a religious viewpoint and I recommend that everyone who is committed to the pro-life cause do the same.
There is a time in the developing baby’s life when there is no brain, no brain waves, no possibility of thought feeling, or awareness. Non-Catholics might identify consciousness and awareness of one’s own existence with “soul,” and until the developing baby has the possibility of that consciousness/consciousness begins to develop, it cannot be said to have a soul or be human.
Nope, not the case. Just because there is “no brain/brainwaves”, doesn’t mean that the developing embryo isn’t human. Humans become pregnant with and give birth to only humans. Not a fish, or a cow, or a two-headed Cyborg from another galaxy.
As far as I’ve read the baby develops distinctly human brainwaves in the second trimester. And obviously once it has them, the baby should be considered human and be protected and have human rights. But until it has them, there is no “person” there, just flesh.
I learned in my embryology class that brain waves are detectable at 40 days post conception. That is MUCH earlier than the 2nd trimester. That’s a little over 6 weeks pregnant from the day of conception; most women don’t even know that they are pregnant at that time. And personhood is NOTHING more than a legal argument. The law gives businesses “personhood” status, the law has denied African Americans personhood status (Dred Scott vs. Sanford), so personhood is a bogus argument. Besides, if your parents are “persons” it stands to reason that you, as an unborn baby, are a person as well.
Normal people will never say that murdering a human being is okay, the question becomes “what is a human being.” For the non-Catholic, humanity might be all about consciousness, the whole “I think therefore I am” bit, not about DNA.
Personally I think all sentient beings, human or not, should have fundamental rights. If we ever developed AI that was self aware, I would support equal rights for it, right to life etc. I think killing apes is immoral because apes show signs of consciousness and self awareness.
To me this is what “personhood” is all about, not DNA. It’s hard for me to believe that a newly fertilized egg is a person because I don’t believe in soul-at-conception. A newly fertilized egg doesn’t think, doesn’t feel, doesn’t know it exists, it has some DNA, some cell components to keep it functioning, and that’s about it.
So? The newly fertilized egg is a stage of development and will continue(if all goes well) on until natural death. Embryo, fetus, neonate, toddler, teenager, elderly—all stages of development. Lack of thinking doesn’t mean a thing(if it did, I’d be in big trouble sometimes

), and nor does lack of self-awareness, etc, etc.