When someone says to me...

...that an unborn baby may be human but isn't a person, and I insist that the embryo is, I like to offer a compromise. "Would you be willing to concede that a fetus is 3/5 of a person?"

..."It's a fetus, not a baby," I point out that fetus is Latin for baby, and it means the same thing in English. Saying "a fetus isn't a baby" is logically equivalent to saying "a thirty year old isn't an adult;" just the same, saying "a fetus isn't a person" isn't prima facie logically different from "a teenager isn't a person."

I've seen many pro-abortionists make the "not a person [yet]" argument, and when pressed to provide some rationale beyond the sophistry I mentioned in the previous paragraph, all the evidence has always been arbitrary. Some of it's been understandable, like basing personhood on the presence of a mind, but it still all boils down to something materialist or utilitarianist, which not every pro-abortionist is prepared to commit to: the mind (sometimes they invent something like "social intelligence" that magically develops at birth even though intereactiveness is observed in multiple births, just like the concious mind they try to get around), viability, maybe the heartbeat, advice from an OB/GYN, or the whim of the mother.

It's not hard to show the conventional artificiality of their distinctions between personhood and non-personhood. Particularly these days, though, it's hard to show the pro-abortionist why such anemic philosophies aren't adequate to defend erring on the side of "The risk of murdering a human is small in comparison," however many caveats they thought to bring to the fight.