The reason religion is so powerful

[John 6IX Breezy]

To the same extent that I know a rabbit doesn't have full personhood because its brain isn't capable of undertaking person-level activities, I know a fetus with fewer brain cells than a rabbit isn't yet a person.

Hmm I don't know much about personhood. But I think you should be careful here. These are some issues:

1. The brain is nowhere near developed at birth; it develops throughout the lifespan. And unless personhood looks like a bell curve, you might be ignoring natural variations across individuals.

2. There are very few cognitive traits that you can't live without. And the parts of the brain that are more life-threatening are hardly the ones doing person-level activities. (And just keep in mind that entire hemispheres of the brain have been removed successfully in surgery.)

3. Psychologists use animals ranging from mice to macaques in the study of behavior because we share many traits with them. I don't know how rabbits compare, but I suspect you've set a deceptively high bar. (Consider that you've potentially removed consciousness as a criteria for personhood.)

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That's just the thing, he said "conception" (fertilization/embryo) which does not necessarily already contain the necessarily qualities to develop as humans (mole embryo).

That there are instances where fertilization goes astray, does not change the fact that new organisms begin at conception. Hamburgers don't stop being made at McDonald's the moment McDonald's accidently puts out a soft taco.