Pro-abortion people often say the unborn baby can’t be protected just because we don’t know he is a baby.   Who is to say?

But in the first place, we do know that he is a baby.  He is an immature member of the same species as ourselves, possessing all the potentiality for further development that a born baby has.

In the second place, the premises you would need to say he may not be a baby lead to unacceptable conclusions.  For example, you might say we don’t know whether anyone is human – but then we can’t protect anyone’s life.  Or you might say that he is human, but not yet a person, because he can’t yet reason, act according to purposes, or speak with us – but born babies can’t do those things either.  Besides, that criterion puts personhood itself on a sliding scale.  For by its lights, if Fred reasons better than you do, acts more prudently than you do, or is more articulate than you are, then even if you are a person, you are less a person than he is -- and so his rights trump yours.  Do you really want to go there?

In the third place, even if we really didn’t know whether the unborn baby were a baby, ignorance wouldn’t justify killing him.  Suppose I really don’t know whether anyone is in the house next door.  Then does my ignorance justify me in firing through the window with a gun?  After all, there may not be anybody there to hit!

You see that not even genuine ignorance would be a reason to abort.  In fact, it would be a reason not to.