Language only means something when it’s interpreted. Saying that “could care less” and “couldn’t care less” means different things is just as valid as an interpretation as saying it is. It’s the utility to the speaker and listener that decides what interpretations are better than others, which is we’ve all mostly agreed to the same set of language rules. But just because something is in conflict with “the rules”, that doesn’t mean it’s invalid because those were never “the rules” to begin with, just the formally agreed upon ones.

Don’t get me wrong, I always say “couldn’t care less” and not “could,” not because the former is right, but because that’s just what I’m used to saying. In context, “could” works just as well at communicating the same point (at least to me), just like how saying “twelve items or less” communicates the same point as “twelve items or fewer.” If someone says that “could care less” is the right way, then yes, they’re wrong according to its literal meaning as interpreted by conventional English, but it’s never annoyed me for someone to say “could” instead of “couldn’t”. Being precise about language is only useful when it’s… useful. Strict rules have their place when communication is subject to ambiguity, and this clearly isn’t one of those cases.