Well the whole thing is ridiculous. And it's something we see on the left quite often - they decide they like an idea then make irrational statements trying to cover for it.If women aren't persons as he says they don't have a chance on legal abortions.
Obviously at some point you have an egg, then at another point you have a human. Virtually nobody thinks an unfertilized egg is a human being. Virtually everybody would say that a 3 year old toddler is. At some point it goes from being one to the other. When it does human rights attach and you can't just kill humans because they're 'inconvenient'. A fact many of my clients benefit from daily.
And that's basically the whole argument as much as the left likes to try to change that channel.
And that's why he stumbled, he's trying desperately to dodge that argument because it is very difficult to make the argument that a child is only a child after it moves that last few inches through the birth canal. Tho some do - and some cultures believe that a baby gets its soul days or more after being born and isn't a real human before then. Just as some believe it gets its soul at the moment of fertilization. But it's a hard case to make.
So the last thing he wanted to do was discuss what a human being is - that weakens his argument. And some how that morphed into saying slaves were considered a person under the law, which he defined as someone who could own property, and that women somehow were not despite the fact many do
Oh what a tangled web we weave.