Okay, here is the non religious, scientific reason to oppose abortion. In the last million years since Lucy lived in East Africa no human female has given birth to a non human. If carried to term, absent trauma, diease, malnutrition, every pregnancy will result in a human being. Now one cannot say with scientific certainty when the entity becomes human, but because we know it will be human if the progressives wish to terminate it they must be able to prove that the entity they are terminating is not human because all the evidence of science and history tells us that it is.
Scientifically, the entity becomes human when the sperm enters the egg and the cell has its own specific DNA. The moment of entry sets it all in motion and the entity is human from that point on.
“Okay, here is the non religious, scientific reason to oppose abortion.”
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And the ethical and purely logical reason:
Since everyone agrees taking an innocent human life is murder, and since there is no agreement on when the pre-born is considered a “human life”, abortion - at the very least - involves the possibility of committing murder.