I expect that this one will elicit strong reactions from certain circles, but here goes ...
Recent discourse on social media has brought to light what seems to be a telling argument against any abortion: that it's a form of murder and, therefore, is considered both illegal and immoral. I have no reason to dispute that abortion kills an unborn person. I prefer not to go down the path of debating the details of when "life" begins or what differences exist between a fertilized egg and a person. I'm happy to leave those arguments to others.
To me, the fact that abortion kills an unborn person is the critical issue, and most opponents of all abortion adhere to the notion that all life is sacred and we should never allow murder to be legal. I'll get back to that shortly, but I want to consider just what it might mean to assume that all life is sacred. For those of us that eat animal flesh, we kill animals (or, have them killed for us and prepared in neat packages at the grocery or served to us in restaurants) all the time in order to feed on their flesh. That bothers some people so much that they become vegans, eating only non-animal foods. But of course, that usually involves consumption of vegetables (and fruits, of course), typically "killing" the vegetation (or at least interrupting its growth) in the process. There literally is no way to avoid ending life in order to survive. In many cases, humans have interfered in the natural genetics of animals and plants to maximize our food production. Many so-called "primitive" peoples went out of their way to "thank" the food from which they derived sustenance in order to survive, through rituals comparable to saying "grace" before a meal. It's the way of nature that life feeds on life, killing the food in the process in order that we can steal its energy to keep us alive. So just how sacred is all life to us? Ever eaten lobster or shrimp or crayfish? How do we eat them? Often by plunging them alive into pots of boiling water! Guess we don't consider their lives to be all that sacred! Other examples abound, including such things as "trophy" hunting. All life is, quite evidently, not all that "sacred" to us if "sacred" is taken to mean that we should never take that life to serve our own purposes.
Can we somehow survive by some means other than killing other life? Unless we learn how to accomplish photosynthesis in our own bodies, this seems to be an unobtainable ideal. At best, we can try to be grateful for the contribution to our lives by our food products and seek to minimize any suffering associated with their domestication and sacrifice of their lives. That's another whole debate of its own and I'm not wanting to go there in this blog. OK, so whatever idealism might be behind the notion that all life is sacred, we must nevertheless kill to survive and the lives we destroy to sustain ourselves are testimony to the fact that such idealism is hopelessly ... well, idealized, and impossible to achieve on a comprehensive basis.
So, if all life isn't sacred, is all human life sacred to us? The fact of the matter is that if we examine our actual behavior and how we respond to our circumstances, all of us can find circumstances in which the taking of human life (murder) is considered acceptable. For example, most of us feel that if someone threatens us with bodily harm, then it's morally defensible to respond to that threat by killing the threatening person. Sometimes we refer to that as "self-defense" or sometimes as "justifiable homicide". I'm pretty confident that by far the majority of the proponents of ending all legal abortions (which won't end illegal abortions, naturally) would accept that murder in self-defense (or in defense of others) is quite acceptable. There might be some debate over what circumstances murder is justifiable, but it doesn't change the fact that murder is "legal" and morally acceptable to almost all human beings, under certain circumstances.
And of course, there's the vast apparatus we have developed to kill humans in large numbers - war. Although there are "rules of war" that can be applied to define circumstances in which killing is not permissible in war, there's the usual debate over just what those circumstances might be. Many people believe that murdering POWs or non-combatants is not acceptable - and yet it happens in all wars on all sides. For war fatalities (that is, the person(s) killed in the process), there's no essential difference. They were murdered, plain and simple. Losing your husband (or father or son, or their female counterparts) to an enemy's bullet has exactly the same impact as if it were done by some deranged criminal on a murder spree. So long as we fight wars for reasons (always of arguable merit), it's pretty obvious that this is yet another situation in which we don't let our notions of the sanctity of human life interfere with killing people "justifiably".
Another exception to the rule is when the death penalty is imposed for certain crimes. Just what crimes deserve the death penalty is always at issue, naturally. People vary considerably in their positions about the death penalty. There's always a sort of inconsistency about the state killing people for killing other people and that bothers many opponents to the death penalty. Some governments feel quite expansive about what constitutes a capital crime, a concept that hardly has remained constant over time. Most of us no longer feel that a pickpocket deserves to die, for instance. Being opposed to Communism or Islam might still get some people killed, however. Not all countries or states have the death penalty, of course, but whether your government(s) allow it or not, many people (some of whom would be numbered among the extreme opponents of all abortion) would find it morally acceptable to murder a child molester (or a cop-killer or a serial murderer or a serial rapist or an abortion doctor), for example, even though the laws of the state have no legalized death penalty.
So, finally we arrive at the issue of abortion. Are there no possible circumstances under which abortion might be acceptable? Not according to some people, virtually all of whom do feel that murdering humans can in fact be quite justifiable - under certain circumstances. Of all the arguments against abortion, I find the "slippery slope" argument among the weakest of them. It seems to me that abortion should not be considered the primary means for birth control, but many (not all, of course) opponents of abortion on religious grounds also are opposed to birth control measures. Nevertheless, if someone can find it possible to accept murder under certain circumstances, they shouldn't be uncomfortable with abortion under certain circumstances. The only thing to debate is just exactly which circumstances justify abortion. Virtually all the opponents of abortion under all circumstances on the "sanctity of human life" argument are being inconsistent and hypocritical.
OK - let the debate begin.