T’Lyn is able to combine all the Tuvixed beings into one creature, which is then described by Tendi as a “Non-sentient blob of meat,” handily circumventing the ethical dilemma presented by “Tuvix”.
It really doesn't. It's like you lobotomising someone before you suffocate them with a pillow. Sure you turned the non-sentient blob of meat back into their constituent parts, but you're the one who created the non-sentient blobs from a bunch of sentient beings.