Because that’s an effective way to argue with pro-life people who get all tied up in irrational, emotional arguments about how “you’re killing a human being”, “it’s a baby, how can you want to kill a cute little baby”, and so forth.
In my opinion it’s very simple. What’s unique and special about humanity is the human mind. Self-awareness, and the capacity to think, and plan, and learn, almost without limit. That is what defines a person. A fetus has none of those qualities, no matter what you call it - a baby or a clump of cells. Its brain is still not operating beyond an animal level.
It is the fact that murder involves the termination of the existence of a human mind that makes murder abhorrent to me, not the termination of the functioning of a bunch of other biological systems.
A fetus does not have a mind. It can’t think, it can’t reason, it isn’t aware of its own existence. I really don’t care if its respiratory and circulatory systems, and other plumbing, are well-developed enough to survive on their own.
What I value is the human mind. If you want to terminate a pregnancy before the baby’s mind has had a chance to develop, go ahead and kill it. It’s worthless to anyone but the parents, and if they don’t want it, kill it.
The “potential” for developing into a person has no value to me. Am I supposed to feel guilty about all the sperm cells whom I have robbed of the potential to develop into a person by not having sex in the past week? Am I murdering countless innocents every time I use a condom? No.
And I don’t want to hear anecdotes of how someone’s baby learned to play Vivaldi on the uterine wall at 24 weeks. Even when they’re newborn, babies have an enormous amount of brain development still ahead of them before they reach mental parity with dogs. And we euthanize dogs on a regular basis when they’re unwanted.
Murdering people is bad. Unborn babies are proto-people of some sort, but not people yet. And in my opinion valuing unborn babies with no minds simply because they exist (sometimes valuing them more than people with fully-developed minds) is the result of a gross failure to recognize what it is that actually makes human life special, valuable, and worth protecting.