Clearly, "ensoulment" doesn't occur at conception. This has been known for a long time, for the reasons you explain.

It is really tricky to declare when "human life" begins. Sperm are alive. Ova are alive. The Catholics used to believe masturbation was a sin because it killed babies (more or less...I'm not familiar with the papal details). But that originated in a time when it was believed that men "planted the seed", and women were the "fertile soil". They didn't know about DNA, and contributions from both parents. Today, if a we regard an ovum as "human life" then menstruation is killing babies. I'm not sure how the Catholics regard masturbation today.

Once it is an implanted embryo, it gets a little trickier. It has the DNA of a full human (barring anomalies). But is it a person? It doesn't yet have a brain (and won't for pretty much the first trimester).

Albaby hates my argument, but I view it in a somewhat legalistic framework. If it's not human life, then everything else is moot. If it is, then we have enshrined in our Constitution that no person may force another into servitude. A woman carrying a baby is certainly in servitude, providing all the needs of the fetus. If she's willing, no problem. If she's not, then anti-abortion laws are forcing her into servitude. While the authors of the Reconstruction Amendments didn't explicitly have this in mind, they also wrote those Amendments sufficiently generally that they (IMHO...IANAL) should apply if we are declaring the fetus to be a person.

So either way, we should not be banning abortion. Fetal personhood doesn't really get abortion foes anywhere, IMO.