You seem to be arguing dubious a position of ambiguity. Can you give an example of what you mean when you say sometimes abortion is not murder and show how it relates to the theological distinction between murder and abortion.
Remember, our faith is not a random collection, but an attempt at a coherent whole. It is not enough to have a consistant view about abortion, that view has to be consistant with every line in the Nicene Creed, and all that they represent.
Now, why do I think this matters. Let’s say you are trying to discuss abortion with secular progressives. And you assert, ‘abortion is murder, it always has been murder, end of story…’ Then they start pulling out quotes, Pope Innocent III specifically ruling that early abortion is not murder, St. Thomas Aquinas arguing the correctness of the doctrine, Pope Gregory the XIV reaffirming the teaching centuries later.
Next you say, ‘well, maybe we believed that once, but not now’, then they pull out documents from the Congregation of the Doctrine of the Faith on procurred abortion and respect for fetal life and point to the actual text and footnotes. And, behold, the same language is there.
So you say, 'well, I’m not up on the whole history of this, but I know what is right, just look at our earliest Christain writings". So they pull out Tertullian, who did have views on abortion remarkably close to our modern ones (although for heretical reasons), and show you that right between two very popular quotes on pro-life websites in another paragragh, one that describes a primitive ‘partial-birth’ abortion in gruesome detail and describes it as a “necessary cruelty”, the moral correctness even the greatest proponents of life would not argue with.
It is really hard to ‘wing’ such a discussion and remain at all consistant. If you want to cite faith as a justification for belief, then it is very helpful to really dig into the beliefs and try to understand and embrace it.
When I discuss my beliefs about abortion with the secular community (which is inevitable, since it is what most secularists now seem to associate with Catholicism), we may not agree, but I don’t get dismissed as inconsistant or hypocritical. In fact, I usually can find common ground on other manifestations on our pro life teachings and get them to concede that my ‘extreme’ views are just a broader, more consistant application of things they already believe.
But this is really secondary. For me the principle benefit is that striving for a deeper undertanding on this one teaching is that it helps keep me more honest with myself. It is so easy to fall into a pattern of moral superiority. ‘No, I’m not perfect, but it’s not like I’m one of those baby killers…’ Such thinking is, I believe, a very poor way to follow Christ.