In making non-religious argumentation against abortion I would submit the following points as presented by bio-ethicists to dispel any logical misgivings that people might have with the pro-life position.
The legitimacy of killing the unborn depends solely upon whether or not the unborn are human beings. If the unborn are human beings, than no argument can justify abortion. Based on this obvious point, it is necessary to explore the common characteristics and the apparent differences between the born and the unborn. In doing so we will hit on the primary reasons why people will dehumanize the unborn.
First of all we know that a person’s genetic material is identical from conception through adulthood. Therefore, we know that the unborn at any stage of development will never be anything other than a human being. It also follows that any person alive today is the same person they were when they lived inside their mother’s womb.
Most people that argue in favor of abortion believe that it is the differences between the born and the unborn that justify abortion. They even go so far as to say that the unborn is not a human being. The only differences between the born and the unborn are size, level of development, environment, and dependency. Obviously, an adult is larger than a child, but the adult’s size does not make him more human than the child. Likewise the tiny unborn human in the womb is no less human because she is smaller than the rest of us. We also know that a small child has not reached sexual maturity and is, therefore, less developed than an adult. The ability to reproduce does not make the adult more human than the child. Therefore, the level of development is not a factor in determining whether we are human beings. If the level of development were the determining factor we could easily decide to kill anyone prior to reaching puberty. The environment or location of an adult does not determine his or her humanity. We are no less human while flying at 30,000 ft. in an airplane, than when we are sitting in the airport. Likewise, the environment or location of the unborn (i.e. the womb) does not make the unborn less human than when it takes its first breath in the delivery room. We must also apply the same kind of logic to the last difference between the born and the unborn. Obviously, if someone is in Intensive Care at a hospital while recovering from an accident, their level of dependency would be significant. No one would argue, however, that the individual was less human during their recovery than before the accident or after the recovery. Likewise, an infant or even a small child is totally dependent on the parents, but the infant and child are considered human beings. The same holds true for the unborn. While she may be in her mother’s womb and may be completely dependent on her mother, she is still a human being. The level of dependency does not determine whether or not she is a human being.
Life begins at conception and abortion kills a human being. Supreme Court rulings do not change the truth. In the Dred Scott decision, the Court declared that slaves were property and not human beings. The Nazis declared Jews and others to be subhuman and non-persons as well. Judicial and political decisions are not always based on facts, truth, or correct moral principles.
I hope this helps.