Pat Greenhouse outlines the case that can be made even from the perspective of liberal atheism, of opposing abortion. This may seem surprising since we normally see religious arguments against abortion, mainly from Christians. However, the point to be made is that the atheist can still see the human foetus as being a genetically independent and distinct new person, coming into existence at conception. The atheist tries to explain this moral worth in various ways, perhaps even having the worth of persons as an axiom, an unproven, but intuitively true assumption. The Christian, in the alternative, sees this unique being as made by God, as part of His divine plan.
In both cases there is a convergence of opinion between two opposite view points on this issue, and that is a very good reason to see the opposition to abortion as fundamentally correct.