By your own link, it's an overwhelmingly religious position. If you look at the issue globally it becomes even more obvious just how religious it is. I'm interested in the exceptions because they are relatively rare.
> Almost every pro-life defense rests on the simple claim that a fertilized egg is human and has particular rights.
Yes, this is exactly the problem. It takes the implications of "human" in well-established ethical systems and attempts to insert the definition of "human specimen" from modern biology. That's not a valid move. Ethicists didn't have embryos in mind when they discussed things like divine rights and deontology.
I'm glad you brought up Aristotle, because he himself wrote on this subject:
"...but when couples have children in excess, let abortion be procured before sense and life have begun; what may or may not be lawfully done in these cases depends on the question of life and sensation."[0]
Aristotle didn't understand the specifics of embryos or implantation, but he was clearly capable of observing that there were stages very early in pregnancy where the thing growing did not yet have sensation, and then further stages where it had sensation but not the sensation of being human. This is astoundingly accurate; props to him.
Applying modern biological definitions to the established ethics of old is anachronistic. You can't just look to the letter of the ancient law and swap definitions from modern, unrelated fields and expect the intent to survive.
You are writing this as if this is not something we already do. Not in the way you mentioned, but in many states and jurisdictions outside America, rape refers to vaginal penetration with a penis. This is an attempt to define sexual intercourse. Other sexual crimes are classified differently (either as sodomy or sexual assault). This is not because these other crimes aren't equally terrible emotionally, but because PIV rape can cause a child, which is considered worse to do without consent.
> In addition to my questions from the previous comment, here's another thing I'd ask Christopher Hitchens (if he were still alive) or those who agree with him on this subject: Is it wrong to have sex with a woman born with a condition that allows her eggs to be fertilized, but leaves no chance for them to ever implant, thereby invariably killing one or two fertilized "humans" every month she has sex? Or, in abstract terms: Is it really the fertilized embryo entity that we care about? Or is it in fact the imminent life? And if it is the imminent life, then why is pulling out okay (or is it)?
I imagine it would be the same as his answer to generic trolley problem questions.
But again, you asked for one example. I gave you one. There's actually plenty of secular pro-lifers, modern, old, etc. You should perhaps read more before just pretending it's a primarily religious position. Ultimately, the Christian position on this (best explained by the Catholic church) comes from Aristotelian ethics, not a particularly Christian worldview, or even one that requires scripture to defend. Almost every pro-life defense rests on the simple claim that a fertilized egg is human and has particular rights. Perhaps the only 'religious' claim the Catholics make is that humans have rights independent of the status of their brains, because humans are made in the image of God. But frankly, if we were to reject that claim, we would be forced to reject the enlightenment ideals this country and secular liberalism were founded upon (most secular philosophers make little attempt to defend why humans have rights in the first place).