I just learned about the remarkable case of Henrietta Lacks, who came down with cervical cancer in 1951. Cells from her tumor are still alive.
I wonder, would pro-lifers consider killing these cells to be murder? After all, this is human life.
The obvious answer is, "No, killing tumor cells is not murder because, despite the fact that they have a full set of human DNA, they are not capable of becoming a fully-fledged human being the way, say, a frozen embryo is."
To which I will respond: but isn't that just a limitation of our technology? After all, bringing a frozen embryo to fruition as a human being is not an easy matter, and would not have been possible fifty years ago. Why is one ball of cells with human DNA better than another just because we happen to have the technology at the moment to bring one to fruition and not the other? Surely moral principles ought to trancend our (transient) technological limitations?