The Memetics of Abortion
Abortion is selected against.
1. How it applies to the Christian memeplex.
Abortions by Christians reduces the number of babies born out of Christian mothers. Christianity depends heavily on parentally brainwashed children for its growth. Therefore, abortion must be heavily selected against. That much is pretty obvious, and that is what we observe - abortion is selected against in most sects of modern Christianity. Only the sects that heavily depend on the support of progressive communities support abortion.
2a. Lack of Biblical support.
In the Bible, the question of abortion was not considered generally relevant. For one thing, life was considered to begin at birth, not at conception, since breathing was considered the standard for life ("breath of life"). Infanticide is promoted by the Bible for ritualistic purposes (see for example Genesis 22:1-14, Judges 11:34-40 and Exodus 13:1-2), as well as discouraged as sinful outside of that context (once again for obvious memetic reasons), but this is not relevant to abortion per se.
Perhaps the only clear example of abortion we have is positive, as God permits himself to kill foetuses in Hosea 13:16 ("their women with child shall be ripped up"). But this kind of slaughter is only used in reference to either war against foreign tribes or wholesale divine apocalypse.
2b. Lack of rational support.
Miscarriage is a natural process. Depending on the age of the mother, misacarriages can occur in 15 to 50 percent of pregnancies, according to Wikipedia.
Miscarriages are also called "spontaneous abortions". But if God created them, then they are abortions on the same level than the actual medical procedure of abortion. So here the Christian loses as well, as he is condemning something that God already created through nature.
There is no rational reason to see abortion as morally negative, or even generally morally negative. Abortion can spare women of the burden of raising an unwanted child, and in more extreme cases like rape, permanent psychological trauma. Abortion, therefore, can be justified by the virtue of responsibility - that one should take responsibility for accepting or refusing to bring a child into the world. It is also part of the expression of sexual freedom, which is to say sexuality without children, which is selected against both because it entails less children and because it promotes physical pleasure.
Note that I said "morally negative", and that this is not a political discussion.
Even though abortion is not an issue in the Bible, Christians heavily select against it for obvious memetic reasons. Furthermore, abortion is generally argued against on the basis of moral or esthetic disgust, which is also an indication of neurosis. This promotes the belief that natural is repugnant (a major thread in Christian thought), like the neurotic rules about menstruations in the Bible.
Abortion is an issue rather like public prayer, in that neither is much of an issue in the Bible (in fact, the Bible comes out against the Christian position on both), but has become a big issue in modern times due to the change of context brought about by scientific or social advancements.
Write in the comments if you think I've omitted something, and I'll add it to this entry.