For that matter, if I preserved my bodily integrity but suddenly was divorced by my wife, lost my job, was deprived of all my financial assets and was shipped to a foreign country where I don’t speak the language, I’d probably have an identity crisis too.
I think the Vatican would file that under ‘relationality’, which OP has alongside embodiment as opposed with the modal rationalist worldview. Family/job/possessions/environment aren’t part of your body, but they are part of your identity. The point being that the “lion’s share” of the self is not contained above the neck, including both other parts of the body and aspects entirely separated from it. As is expressed when people say, “when my beloved died, a part of me died with them”, or, “I poured my heart and soul into my work”, and things like that.
But, after thinking about it some more, maybe this is a less important/relevant objection than: wait, if we’re comparing humans to AIs, why are we stopping at the neck? Why not include in embodiment the brainstem, cerebellum, endocrine system, occipital and parietal lobes… anything dedicated to motor control, balance, most sensory inputs, basic unconscious bodily functions, hormones, or more-or-less anything besides abstract cognition and language? If these were all destroyed and I somehow didn’t die, I might still be able to produce text (at least in my head, though I’d surely be a vegetable to the outside world), but it absolutely seems like a huge and irreplaceable chunk of myself has been lost. And current AIs do not have analogues to any of these, excepting (very poor) visual processing on a few of them.
As you say, large parts of the human brain are only active in the context of being attached to a certain kind of body. What the Church is comparing here are not really embodied-humans vs. brains-in-jars, but embodied-humans vs. a-relatively-small-fraction-of-the-brain-in-a-jar. This seems more interesting to me. I’m not sure you can abstract away all of those things, all the muscle memories and twitch reflexes and coordination skills and sensory responses and inputs from various glands, and still have a complete human brain at the end. Even Stephen Hawking had to get very good at twitching his cheek.
Also, I don’t know if you did this on purpose, but:
Relativity and quantum mechanics may both be mind-bending and baffle the understanding, but no less than when a world-famous mathematical and scientific genius who can do little more than twitch his cheek and move his eyes; who cannot feed, dress, wash, or care for himself in the most rudimentary way; who would, if abandoned next to a stockpile of food and water, starve and eventually die of dehydration where he was left, positioned as he was left, tells us that there are “not that many” things he cannot do.
...the opinion that Hawking was, in fact, lesser for his condition, is right at the start of the thing I linked. I don’t agree with all of what’s said in 2arms1head, and I certainly don’t think Hawking was any less worthy of moral concern for his ALS, but I sympathize with the notion that paralysis of the body destroys an important piece of the self.
...why shouldn’t engineers play Factorio?