In skimming through the Anglo-American legal history of abortion and feticide, I have come to the conclusion that the killing of an unborn child has only recently become the object of severe opprobrium.
The 13th century jurist Henry de Bracton wrote,
A fetus is "quickened" when it begins to move in the womb, which means that this law applied only to more mature fetuses. Moreover, according to the 18th century jurist William Blackstone, the ancient law of homicide to which Bracton refers was equivalent to our manslaughter, and not murder.
From Bracton to Edward Coke, the common law seems to have relaxed even these restrictions, adopting instead the Born Alive Rule, which still applies in a minority of the United States.
Thus it seems that the modern anti-abortion movement is, insofar as it classifies abortion as murder, at variance not only with the legal tradition, but also with portions of the orthodox/catholic and protestant traditions.