"If oysters - lacking a CNS - react to external stimuli and quite probably "feel" something, even something as basic as lack of food, shouldn't we abandon the idea to live without hurting some other living being?"
Some have already abandoned that idea. I quote Joseph Campbell[1]:
"Life lives on life. This is the sense of the symbol of the Ouroboros, the serpent biting its tail. Everything that lives lives on the death of something else."
I've always felt that sustaining oneself with the life another animal or plant or whatever is the ultimate sign of respect and should be considered an almost sacred act.
Some have already abandoned that idea. I quote Joseph Campbell[1]:
"Life lives on life. This is the sense of the symbol of the Ouroboros, the serpent biting its tail. Everything that lives lives on the death of something else."
[1] https://en.wikipedia.org/wiki/Joseph_Campbell