The issue is not whether they are human or not; but whether they are viable - able to live on their own.
Why is "viability" the proper criterion? And what is it a criterion for? The definition of life? The definition of human organism? The definition of murder? "Viability" seems a thoroughly arbitrary place to draw the line. What makes it normative?
It makes a whale of a difference whether a procedure is an abortion or a pre-mature birth. Taking a child out of the womb at 10 weeks is an abortion. Everyone knows that the child will die. Taking a child out of the womb at 24 weeks is a pre-mature birth. The child will likely live.
Or, when removing life-support. If the patient is capable of recovering (i.e., viable), it could be seen as murder. If the patient is not capable of recovering (i.e., not-viable), it's an acceptable step.