Disclaimer: I was born and raised Lutheran but am no longer religious

Through a religious lens, it seems these arguments are proxies for "killing a soul bearing being." The key problem is a soul can't be detected - we don't actually know what carries a soul and what doesn't. Through the non-religious lens, the question is what constitutes a being with human sentience. At what point does a collection of cells cross the threshold from a chemical machine to whatever Descartes was referring to when they said "Cogito, ergo sum." Humans are pretty far away from understanding the phenomenon of sentience; AFAICT we don't even know where to look for it. I observe the universe - but I don't know where that "I" came from, where it goes when my cells die, how a random collection of molecules became attached to that "I," or how it stays attached as my cells cycle out throughout my lifetime,

Back to the religious take - depending on when you believe God has endowed a collection of cells with a soul is the moment you would consider stopping that process "murder." This, IMHO, is where things get problematic: that belief is a guess and getting it wrong has pretty massive implications under religion.

An example taken to the extreme: if God allocates a soul ahead of time, stopping a human from coming into the world could be a sin. In other words - abstinence would be preventing a soul from descending to this level of existence. If you abstain from the urge to produce a soul bearing being, and that soul had been allocated, what happens to that soul? Getting this wrong means you could be committing the same sin as "abortion" every time you abstain from an urge to procreate.

On the other extreme: What is special about the moment the Gametes meet? Why would that be the moment a soul gets allocated? Or when the heart beats for the first time? Or when long term memory develops? Getting this wrong means you are doing a pretty great harm to humans for something that may not be a sin.

From the non-religious perspective, I have no idea why my collection of cells is so particularly special that I was endowed sentience when other forms of life aren't. The easy one is human-like meat. Pigs, cows, horses, dog, cat, etc. I see no reason why something so similar to me wouldn't be sentient or why that sentience shouldn't be protected. But it doesn't really stop there - I have a hard time understanding why cows should be so special to be endowed with sentience while a palm tree or tomato plant isn't. I often think about the asparagus in my fridge and wonder if it "died" when it was harvested, or if it is a sentient being slowly starving to death in my refrigerator. Which then leads me down the ethics of consuming any organic molecules - is life just one big murder-dome in which sentient beings compete with one another to be the one that does the eating and not the one that gets eaten?

If you're still with me, I guess what I'm saying is it's messy and people are just guessing. At the end of the day, I wish we could own that these are guesses and approach the conversation with a bit more humility - it's very likely all of us are wrong (myself included) about this entire argument.