The first reason not to is the plain fact that it's not true. Saying that a sperm piercing the exterior of an egg is the beginning of life in a scientific or legal sense, would require you to say that sperm and eggs on their own are the beginnings of life. Then what, women are no longer allowed to be anything but pregnant? Men must save every sperm for a future baby? The truth is that human life as we know it starts when the bundle of cells actually has a body, a functioning heart, and the start of a developing brain. All of those things don't happen together until about mid-second trimester, which is when abortion is illegal anyway. Protect and help the already living, not bundles of cells that mean nothing to you and could mean living in poverty or poor health for someone else. If you are female, you have the ability to become pregnant and therefore have an abortion. So, if you are female, either use the proper birth control, have an abortion, give the baby up for adoption, or go through with the pregnancy. No matter what, it is the woman's choice because it is the woman's body. Men who disagree for some reason? Either don't have sex with her or use a condom. A woman can't get pregnant without a man's sperm.