This issue is fraught with the difficult realization that logic at it's heart is illogical. It is perfectly logical to conclude that life begins at conception: that just seems so natural. But that, coupled with the notion that life is sacred, leads to the irreducible paradox that a woman must be a prisoner to a fact of nature wholly accidental in evolutionary origin, namely that she conceives not by choice but by the presence of fertile sperm surrounding her fertile egg in sufficient numbers, regardless of how they got there. Such an absurd state of affairs tells us that we can't be logical and solve these emotional questions. Life is sacred because life is sacred when there is consciousness aware of that fact. This may mean that it is the consciousness that is in part sacred. It seems therefore that we project our own feelings of the awareness of the sacred on the fertilized egg and make of it an idol to which we will force women to bow.
Such a paradox is illogical and something, it seems, should give. I would say, therefore, that for the sake of the conscious woman, we cannot make an idol of her fertilized egg and must look at it only as a bundle of animated chemicals that are organized via billions of years of evolution in a particular way. We don't want to abandon the notion that life is sacred, but we don't want to make ourselves prisoner to it where to do so also leads to evil. Women need to be able to have children when they want them and also engage in sex as they choose. Clearly what is needed is sex education and efficient contraception so the issue arises as rarely as physically possible. Children should be born by choice, logically, but evolution had other ideas, since choice was late to the scene.
It strikes me as absurd that religious beliefs, doubtlessly founded in the need for soldiers and cultural expansion, should govern an over-populated earth.
This is, of course, at the heart of the stem cell issue and why religious limitations there are also insanely illogical.
The fear, of course for an absolutist, is that if life isn't sacred in certain cases it never is. That is a threat to faith, of a rather shallow kind, and threatens their belief in immortality and heaven. So for the sake of the wish to live forever, we will gladly ruin the one life we actually know that we have. But of course it's not our own life we wish to ruin, but the life of others.