"But the machine-implemented facial recognition faculty of Facebook is, presumably, far more capable than the slug's probing tentacles to draw nuanced distinctions about its environment. [???]...So then why do humans claim to be conscious while denying consciousness to Facebook's facial recognition algorithm? "
That is projection.
To say that "Facebook's facial recognition algorithm" is conscious is similar to saying that the mathematical expression 5+7=12 is conscious. Who is "conscious" here are the species that use this equation and the engineers who created recognition algorithms.
I will believe that this recognition algorithm is conscious when it reacts to ugly or disfigured faces in this manner: https://agaudreault.files.wordpress.com/2020/10/baby-expression.mp4 , or when it shrugs when asked to give the address of a Jane Doe.
A facial recognition algorithm that differentiates between two lookalikes is as conscious as the camera that takes the picture.
A good definition of consciousness is Daniel Dennett"s: "...consciousness arises from interaction of physical and cognitive processes in the brain."
A piece is missing here: There is no "cognition process" what so ever in neither a camera nor an algorithm.
Another useful saying is "To live is to Know" Found in Humberto R. Maturana's "The Tree of Knowledge."
Thus, data engineers play God or Frankenstein when they believe that their algorithms will eventually make their machine alive.