I'm waiting to hear a counter-argument that doesn't boil down to "life begins at conception because that's when it starts."
Life began 3.6-3.8 billion years ago and hasn't stopped since. The sperm cell that fertilizes the egg is alive, the egg itself is alive, and the cell division and reproduction that occurs soon after is proof that their product is alive.
So the question about when life begins is a false one. Instead of trying to redefine what is life for the sake of makingabortionsound more appealing, we should simply accept that termination of early stage human organisms is legal. That is what we are doing. Without such interference those organisms have a good chance of becoming mature humans.
However, I believe there should be a point of no return. That once a human has matured past a certain developmental stage, that's it, it has a right to live. The point itself is arbitrary; but I think it should at least create a buffer between when abortions are allowed and when a baby would be viable if it were to be born prematurely.
Why create such a point? To clear up potential ethical dilemmas involving unwanted children that might be viable without the mother. The mother is saying terminate, but the technology could allow the child to survive in spite of her. Do the mother's wishes override everything? Should she be given the power of life or death over the baby until the umbilical is cut?
The vast majority of abortions take place before 13 weeks from the last menstruation. The earliest baby to survive I believe was at 21 weeks 6 days. Technology will continue to close this gap until a human organism will be able to be grown entirely outside of the womb. It would be much cleaner to have a definitive cut off date after which embryos are protected.
But all of this only really applies to the arbitrary decision to terminate because the mother does not desire the child. The medically necessary situations (which are rare) should not be subject to such a limit. Nothing should get in the way of a doctor's ability to make decisions for the survival of his patients. But choosing not to recognize a life because someone does not wish for it, is deception. We should simply be honest about what it is we permit in our society.