[kmm]

Who cares if it has a "logical error", whatever that even means, if you understand. And I know you understand it.

Millions of people use this idiom completely intuitively, following their instincts of language that I, as someone who doesn't have English as their native language, can only be jealous of.

"I could care less" is either meant to be taken sarcastically, or it came to be because the "dn't c" consonant cluster is hard to pronounce, the same reason you don't pronounce the 'l' in could, the 'k' in knee, knight or knave, the 'p' in psychologist or pneumonia, or half the letters in Wednesday.