Fetuses and Babies
Here is a thought experiment: Think of a mother on the birthing table at full term, normal pregnancy. Is that a baby in the birth canal? You know it is. Now go back a week. Is it still a baby? Carry this on for a while. Where does it become not a baby? How far back in the development of the nine months do we go to declare it is not a baby? I have heard doctors of OB/Gyn who have become anti-abortion, changing their mind from pro-abortion, and they say that this thought experiment is what brought them to be against abortion. They know that development of the human fetus is a smooth continuum. There isn't a "bar mitzvah" in the womb - no great change from one thing to another - it is all very gradual - and so impossible to pinpoint a day, or week, that the fetus changes into a human being, into that baby in the birth canal (and the day and the week before birth etc.... )
The "big bang" days are conception and birth.
In light of this smooth continuum of development in the womb, we must face the fact that if we want to be reasonably logical, then to answer the question of 'when life begins,' we have to pick one of these:
If we say that 2. birth is when this thing becomes a person, then it is totally logical that abortion should be allowed during all nine months of pregnancy and it should be without moral trepidation. The people that advocate that partial-birth abortion is OK are actually being consistent with their belief that BIRTH makes someone a person.
On the other hand, if we say that 1. conception is when life begins, then that brings obvious implications with it and a drain on the idea that abortion is OK and without moral consequence.
Now, if you hold that birth is when the fetus becomes human or a person, why would we say that abortion is to be avoided or curbed?
One more thing: You said calling this a baby is: "emotive and sentimental (even manipulate) language."
When I was pregnant with our fourth child a couple of years ago and my other kids were 6, 8 and 10, they looked at the 20 week ultrasound and they said it was a "baby." It is common to call what comes out of the womb a "baby". I don't think this is emotive language. It is consistent with the view that life begins sometime before birth.
I think using the word "fetus" in lay discussions evolved in these last decades to avoid guilt over the fact that people knew that the mother on the delivery table (in my thought experiment) is delivering a "baby." I would say that using the word "fetus" as we do today is to make abortion seem morally permissable by trying to squelch the basic human tendency that we have to protect those who are the most vulnerable in our species: babies.