Round three of Heschmeyer vs. Dillon on abortion:
So on one level this debate is a kind of Imperial Star Destroyer vs. USS Enterprise match, an argument devoid of substance that refers only to fictional entities like "souls" and "metaphysical humans". On this level Heschmeyer's argument is biologically ignorant: a live person and a dead person are not identical other than for some missing "animating principle"; the dead person is dead because physical changes have prevented the continuation of the processes that normally occur in the live person (and which do not require any separate principle to sustain them because they normally sustain themselves and each other).
At another level, Heschmeyer continues to deploy items from the range of dishonest rhetorical tropes common to anti-abortion argument. In ordinary English usage "murder" refers to the malicious and unlawful or unjust killing of a person; if abortion is not malicious, unlawful or unjust then it is not murder. Claiming that an argument for abortion is of the form "murder isn't always wrong" is to both presuppose the desired conclusion (that abortion is murder) and to dishonestly smear the opponent by connotation. If we reword it as "killing isn't always wrong", we get a much less controversial statement.
We value human life. Why? Without an honest answer to this question, one not involving fictional entities (and also not neglecting the emotional basis for the answer by pretending that it's just metaphysics—emotions, including moral emotions are real even if they're not necessarily an accurate guide to morality), we can't get at the root of the argument.
(Me, I think we value human life for reasons that depend on (a) the person's consciousness of their own future and (b) the person's relationships to other persons. It is entirely consistent within these values to consider abortion as not contradictory to either.)