In my previous post, I argued that many of those who disagree with us that abortion is wrong already implicitly or explicitly admit that the fetus is a person. However, some who come from a philosophical angle would argue that the fetus is not an actual person, and therefore, while biologically alive, is not morally equivalent to a human person. They deny the personhood of the fetus based on a functional definition of personhood, that is to say, what makes an entity a person is whether that entity can do things or exist in a way that human persons can (for example, a human person is capable of reasoning). A necessary implication is that any entity that loses or does not possess these functions and attributes is excluded from personhood by virtue of the bounds set by the definition.
There are problems with this way of defining personhood, leading us to some uncomfortable or even absurd conclusions, as this article outlines well. I heartily recommend you read it in its entirety.
As Christians, we cannot accept any functional definition of personhood and consequently make moral status dependent on function because we believe that human beings are deserving of protection of life simply because they are made in the image of God (Genesis 9:6). It is what makes human beings special. Nothing about what the person can or cannot do enters into the equation. The severely mentally impaired child is as much a person as the successful CEO of a multinational corporation. As Christians we affirm the intrinsic value of all human beings everywhere, for all people are made in the image of God. Every individual human being, therefore, is valuable and deserves not to have his or her life taken away as long as he or she is innocent of any crime worthy of death, such as murder. Therefore, he or she deserves protection from anyone who would come and take his or her life away. This status cannot be lost if the person falls into a comatose state, or a mentally deranged condition, since his or her moral status is not in any way dependent on functional attributes.
As a consequence of the moral status of all human beings, we are not guilty only if we kill an innocent person; we are also guilty if we stand idly by while an innocent person is being killed right before our very eyes. In fact, we instinctively feel more moral outrage when a wrong or injury is done to someone who is weak or defenseless. How much more should unborn children be protected; those whose screams we cannot hear, those whose pain we cannot see, those who cannot protest against slaughter and injustice?