Argument against abortion

 Some variant of this argument still seems to me to be the best argument against abortion (I think I got the original version in a video from Matt Fradd from Pints with Aquinas, and I'm not sure if he invented himself or if he got it from elsewhere; but in either case I've adjusted it to some extent, but the over arching form remains): 

1) Intentional Killing of innocent and helpless human beings is always wrong, regardless of circumstances and intent.
2) Direct abortion is an intentional killing of innocent and helpless human beings. 
C) Direct abortion is always wrong, regardless of circumstances and intent. 

Premise 1 seems to me to be a more or less self-evident moral principle; a man ought rather be willing to sacrifice his own life before he would kill someone who has done no crime (is innocent) and who cannot defend themselves (is helpless).

This rule is quite permissive: a man going through a psychotic break can defend themselves, as surely can sane but malevolent assailments, for though they do not have reason, they do have some degree of awareness and instinct to fight; but if you find someone chained down or unconscious or in some other state where they cannot act to defend themselves, and they have committed no crime, then you should sooner die yourself than take their life. 

Anyone who would take someone's life in such conditions would become a moral monster, a being deserving of eternal torment and damnation for such a grave affront on human dignity, for humans are rational animals, we have our special dignity in our capacity to embody, especially through speech and deed, various transcendent and abstract realities, so that our bodies and bodily actions serve to reveal such realities; and so even to reveal a value, and so even infinite value; and as this is our nature as whole beings, so there is a certain infinity to the value of human nature and so to the value of each human; inherent within our nature, which our living bodies exemplify; so that to take the life from our bodies is to deprive the world of a certain infinity of value; man is the microcosm, so that to kill a man is akin to killing a whole cosmos; thus we may never take this killing as our intent; but rather are obliged to do all we can to avoid it, even to give up our own lives for that end.

The reason for this is that to form an intent, and especially to act on an intent, is also thereby to form one's character; since by one's free will (which one's intent and actions are an extension of) one chooses not just what intent and act one will do, but also thereby chooses to 'become the sort of person who would' choose such an act and intent i.e. one's willed choices and commitments to intent and action all serve also to form one's 'moral character', and to intend to kill a human being is thus to become the kind of being that would destroy things even of infinite value; there is, quite litterally, no limit to the depravity of such a moral character. It is rightly called monstrous; and by any measure; it is better to die a good man than to live a monster, so likewise all sane, rational, honest, and moral men ought to stake their own lives on never committing such an act. 

For to commit such an act is clearly to go beyond the pale; and nothing short of sincere, sorrowful, and heartfelt repentance, conjoined with divine pardon (that is, the pardon of a being infinitely more intelligent and powerful than any human being, and to whom all human beings are in infinite debt, so that no man would have a right to contest such pardon in light of their debt) could relieve one of the stain on their character; and as such pardon is either impossible (on atheistic views, or theistic views in which God is not so quick to forgive) or at the very least 'not guaranteed' (on all non-presumptuous theistic views, and so any view in which there exists a God who takes human dignity and injustices against it seriously, and so, any view which is worth having by the standards of human reason) then there is no moral calculus that makes it worth the risk i.e. such an act is inherently 'inhuman' and so therefore also inherently contrary to human reason, and so inherently irrational; there is no evaluation that is at once 'true' and will also say such an act is worth doing. 

(To note though, this all has to do with intent and intent based acts; as such, not all killing is forbidden, for some killing is done not intentionally nor by negligence (which would make one monstrous by neglecting something of infinite value) but rather by a kind of aknowledgement of an inevitibility 'despite' trying to avoid it; thus one who works to protect their own life or the lives of another from an assailant and uses force one recognizes is apt to result in the death of another, does not thereby intend to take infinitely valuable lives, but on the contrary, intends to preserve them; but realizes that in doing so, there is an unavoidable side effect of a loss of equally valuable life; if the side effect were avoidable, one would be obliged to avoid it, neither could one justify saving a life 'by means of' taking another; instead, the 'means' are the means of necessary force for the defense of life, it's just noted that the act of using that force has two effects; the one of saving a life, another of losing a life; and the latter is not avoidable for the former; and the later was the thing that was, by it's own power and will, making the former necessary. 

Naturally, someone who is not by their own power and will putting another person's life in danger may not be killed; thus if a villain sets up a room so that if you don't kill an unconscious or chained down man, then then the automated turrets in the room will kill you; you are obliged not to kill in that circumstance, even if it means you die; for again, killing an innocent and helpless human being is always wrong, 'regardless' of circumstance. 

Mind, it's questionable as to whether all people would be coherent enough in such a circumstance so as to 'form' a coherent intent; but that would only mean that if they killed them, their culpability was reduced, so while they would not become a monster in doing so and so would not deserve the fate of all such monsters, none the less the act would still be objectively wrong, even if they don't deserve the full punishment proper to the act; but for someone who, despite the stress, can retain full possession of their faculties, if such a person were to kill, they really would become a moral monster in doing so.) 

Premise 2 
To kill is to cause death, either intentionally or by neglect; and death is the separation of the body and whatever may truly and intelligibly be said to give and sustain life to that body (whether that be a certain bio-chemical process, a 'soul' or 'spirit' or what have you, death is the separation of this from the body). 

Now a body is alive insofar as it undergoes some sort of immanent activity, which is to say, some sort of activity which serves to make the body grow into a more mature state, to keep the body whole, and to restore itself to wholeness when sick or injured i.e. any activity which is inclined towards the preservation, perfection, and/or propagation of the whole; the activity thus being called 'immanent' because it's inclined towards something to do with the whole, rather than to something outside of the whole. 

We categorize a living body as a member of a given biological species precisely when it has DNA similar enough to other members of that species to be united with them, and yet differentiated from members of all other known species. 

(Typically, this DNA is still distinct enough from members of the same species to be differentiated from them; though there are perhaps exceptional cases such as identical twins and species which clone themselves; in which case their DNA still identifies them as members of the one species and separate from other species, but they are identified as distinct individuals not through DNA alone, but also through other physical differences, such as differing spatial location or such like; but in either case, identification of species membership occurs via having similar DNA.)

In sexually reproducing species; the formation of such similar DNA occurs precisely via the process of fertilization; where DNA distinct from either parent is formed. As such, at the moment fertilization is complete, a new member of a species is formed. If that DNA is human, then at that moment a new member of the human species is formed. 

Of note is also that this individual is also begins the process of cleavage, which is akin to cell division, and so serves to perfection of the whole body; as these processes are all inclined precisely to bring the organism to further and further stages of embryonic development; and so have to do with bring growing the whole body to greater maturity; this is a typically immanent activity, so that the entity is alive. 

Thus, we have an entity with DNA distinct enough from it's parent to be considered a separate organism, and so a whole in it's own right, which is in fact alive due to going through essentially metabolic processes. 

Now all distinct human wholes are distinct human persons, so that at the completion of fertilization, we have at least one distinct human person. (possibly more, if the organism is disposed to bring about twins or such like.) 

Now direct abortion works to end the various processes that begin at fertalization onward and which are aimed at the development of the human person(s), and as these processes are what keep this human person(s) alive, then abortion aims at death of the person(s), and as such an aim is killing, so it aims at killing the person(s). 

Now the at no stage of pregnancy, from fertalization to birth, does the organism(s) in the womb have any more ability to defend themselves nor commit a crime than a born infant does, but an infant has 'no' ability to commit crimes and defend themselves; neither than does the unborn; as such, the unborn human person killed by direct abortion is innocent and helpless. 

Thus, as was said: Direct abortion kill the innocent and helpless human beings. 

The conclusion follows.