Ah, abortion, knew we'd get to it sooner or later.
As Oscar points out, much of the debate is fruitless because we tend to have conflicting presuppositions. Or, more technically, we are operating from different mythos.
One of the enduring elements of the American mythos is the rugged individual. That great American that we all picture ourselves to be who was wise and judicious in choosing his place of birth, careful in his selection of parents, prudent but ambitious in picking out genetic potentials, who changed his own diapers and suckled himself (or mixed the formula), and grew to become a captain of industry: happy, wealthy, and wise.
In short, the self-made man (or woman) who doesn't need anybody and for whom all of society's demands are so many lampreys, leeches, and other assorted parasites sucking away the fruits of his accomplishments as he drives on roads he paved himself in the car he made himself by smelting the iron ore, learning the principles of an internal combustion engine (oops, I mean *inventing* the principles of internal combustion) and so on and so on.
In other words, bullcrap. Any individual American knows that "no person is an island" but we simply do not have any cultural understanding that like it or not we are all in this together!
So what does that have to do with abortion? It comes into play if you have a different mythos, a mythos of community and culture, in which you believe that you have obligations and duties to collective society, and that you benefit and suffer with society whether you want it to be true or not.
So, in the community mythos, the children my wife bore to me are ours not hers. She and I form a community of two, which gave birth to a wider community of five. I have very real obligations to that community, which sometimes feel burdensome, along with tremendous blessings that always obliterate the random burden. In turn we belong to the community of our neighborhood, the local church, the city, state, nation, and world. We can never escape the burdens of membership at any level, and every day we enjoy the benefits.
In this light it is not possible to see a pregnant woman in isolation, or to imagine that "the penis bearer" can be separated from the discussion. If she and he are entrapped in the individualist mythos then they will see themselves that way, more's the pity, as they put themselves beyond not only whatever help may be available in this or other situations, but they detach themselves from the joys of making real contributions to their various communities.
It is particularly difficult to weed out the actual religious perspective because it is usually wound up in the individualist mythos and so distorted beyond recognition. In the Christian perspective the unborn child is not innocent because that implies the very ability to be guilty of something. Rather the child is defenseless, and, while most people do not know this, if you want to hear some real old-fashioned smiting and smoting in the Bible, you will find it is nearly all directed at the powerful who abuse their power at the expense of the defenseless. The simple-minded conclusion here is to blame the woman, as she so obviously has power over the child, but that is balderdash. In this perspective, where "to whom much is given much is expected" the burden is on those in a position to render aid to do so, both to prevent the situation in the first place, and to bolster the woman once it has happened. Ironically, it is typically the poorer churches that tend to "adopt" the unwed expecting mother, while in the wealthier Churches, which are more in the grip of the individualist mythos, the mother may disappear for a few months because she knows full well there will be no material support but there will be a healthy dose of clucking and judgment.