Sagan soundly addresses many of the peripheral questions that are often substituted for the real questions of abortion "When is a baby human?" and "Is murder wrong?"  If you are at all confused about the surrounding issues, Sagan's article is of tremendous clarifying help. However, the inevitable questions still arise. Sagan does answer the 1^st question, though his answer is more than an individual opinion – it is the natural conclusion of his philosophy, one might even say of his religion. The second question he only discusses briefly, because few people would ever assert that murder is right.

Sagan is a self-avowed humanist. Humanism is a religion based upon atheism, though human accomplishment and potential are actually the object of worship. Logic and science substitute for faith. Spirituality is denied; thoughts and emotions are merely complex chemical reactions with evolved and conditioned ulterior motives. Still, humans are uniquely creative, and the ability to create requires thought. Therefore, the physical basis of thought is the highest form of human essence that a humanist can conceivably believe in. There is no soul, no spirit, no eternal or transcendent substance to an individual. This flows logically from a disbelief in God and the afterlife. Therefore, Sagan’s argument is logical; though like all logical arguments it flows from an accepted premise. However, if one does not accept the initial premise, the argument is meaningless. Although the afterlife cannot be scientifically proven, it also cannot be scientifically denied - therefore Sagan's premise is an unscientific one. I do not condemn unscientific premises, I often use them myself, but humanists have a definite preference for the scientific.

Moral relativism has become popular in recent decades, and it is worth pointing out a connection between relativism and abortion. When considering the argument under this light, the crucial question becomes "Is murder wrong?" If you really examine relativism, you will find that there is no real right or wrong, merely actions that are socially accepted or unaccepted. Societies naturally find murder unacceptable because it fundamentally threatens the existence of society. Individuals fear society because there is power in numbers. This has reduced the argument to one of  "might makes right."  Humanism rejects absolutes, accepting moral relativism. The result is a timid hope in the basic goodness of one's fellow man:

How should that problem [of justice] be solved? I know of no answer that could satisfy everybody. Having different, perhaps even incompatible, interests, we all wish to maximize the achievement of our own ends. Therefore, if I told you how the problem ought to be solved, if I laid down my ideas of "justice," I would be doing no more than trying to get you to accept a set of principles that would maximize my interests. Instead of putting out that kind of dishonest propaganda, I prefer to engage in open and forthright communications: let me have things partly my way, and I won't stand in the way of your having them partly your way. The alternative is to fight, and I'm a coward. 

-found in Understanding the Times by David A. Noebel;

original source Hocutt, "Toward an Ethic of Mutual Accommodation" 

But there are those who will fight; Marxism/Leninism rejects absolutes and can then adopt a conceited form of moral relativism. The result is a blatantly arrogant claim to the sovereign goodness of one's own views without appeal to any higher authority:

Our cause is sacred. He whose hand will tremble, who will stop midway, whose knees will shake before he destroys tens and hundreds of enemies, he will lead the revolution into danger. Whoever will spare a few lives of enemies, will pay for it with hundreds and thousands of lives of the better sons of our fathers. 

-found in Understanding the Times by David A. Noebel;

original source Nikita Khruchev, Ukrainian Bulletin, August 1 - 15, 1960

Cited in Bales, Communism and the Reality of Moral Law

The Judeo-Christian ethic (and Islam to an extent) does not really do away with the "might makes right" argument. It simply levels the playing field for humans by invoking the righteousness of an almighty God. From this principle comes "…all men are created equal and endowed by their Creator with certain inalienable rights" (the Declaration of Independence). For certainly, it cannot be logically asserted that all men are evolved equally, or that evolution can endow inalienable rights. This is the basis of much American ethical thought, and messing with this foundation seems a dangerous business to me.

Humanism gives one answer to the question of when a baby becomes human - at the time when he is able to think (when he can begin to comprehend logic and his own existence, the faith and deity of Humanism). Creationism says at the time the soul is recognized by God. Both of these answers have religious origins, and I think it would be impossible to come up with an answer that has a non-religious origin. There is only one answer, however, to whether or not murder is wrong, and that is when some power declares it to be. However, only a view that accepts God can unequivocally assert that abortion is wrong. No other view has the authority to make such an absolute claim - and not surprisingly very few others will try.

My Take

Psalms 139:13-16

The natural conclusion of these two verses leads me to accept that the Bible asserts the existence of the soul (which is that part of us capable of responding to God), at conception, and perhaps even before. If you want a scientific corollary, the DNA is formed at conception, and that is not only of a uniquely human pattern, but also a uniquely individual pattern. Sagan himself states that egg and sperm are alive, and I would advance that at conception an individual human life therefore exists. Because of "Thou shalt not murder" (murder being defined as one human being deciding without right of authority, differing from, say, capital punishment, or war) to take the life of another, I conclude that abortion is wrong.