The legal question to me should hinge not on conception but on implantation. Human life begins at conception because it can begin at no other point in time. However, pregnancy begins at implantation. Abortion ends pregnancy by killing the fetus. That tells me all I need to know about abortion to know it is evil, and when a person has an abortion to end a pregnancy, they have killed a human being.
A simple positive pregnancy test is all that is needed because abortions aren't performed on people who are not pregnant. Case closed.
Most fertilized ova never implant; of those that do, about a third to a half fail to grow. Only 10-15% of fertilized ova are capable of growing into a full-term baby.
This is one reason I don’t like using fertilization as a marker of the “beginning” of life. The fact that there is nothing unalive at any point is another: living human ovum+living human sperm=living human zygote (even if it dies within hours).
Implantation, to my mind, is a logical time to extend the full protection afforded to born human beings to the unborn human.
A woman who wants to avoid pregnancy has a number of options that prevent fertilization and implantation. There is absolutely no excuse for not using those options.
Re: “...because abortions aren’t performed on people who are not pregnant.”
That is not quite true. I’ve heard that abortion mills sometimes lie to prospective clients about the results of pregnancy tests, so as to get them to undergo the procedure anyway. It’s all about the money.