I believe the term 'could care less' is largely facetious-
"I could care less... but it would be extremely difficult," tends to be the implication; don't understand why you found it necessary to correct him.
Eh, I think it's just a common mistake, and I corrected them because it's a pet peeve of mine, not because I think it is a big deal. Your line of thinking is not new to me though, and if "could care less" is sarcastic then I would argue it is particularly ineffective sarcasm (see: http://incompetech.com/gallimaufry/care_less.html).
It's no longer a common mistake, it's now become an idiom in some dialectic variations. As such it cannot be broken down into its constituent parts and analyzed for meaning, it has to be understood as an atomic utterance. It's a little like "The proof is in the pudding." The original was "The proof (test) of the pudding is in the eating," but it got shortened, possibly by mistake, possibly by laziness. And so it is with "I could(n't) care less."
It's like sandpaper on my brain, but that's how linguistics works. The more you study language, the more you realize it can't possibly work.
> As such it cannot be broken down into its constituent parts and analyzed for meaning, it has to be understood as an atomic utterance.
I understand the implicit preface that is something like "If you want to communicate frictionlessly …", but I think that one actually doesn't have to do this. The arguments for accepting variants of spelling do not, I think, automatically apply to accepting (illogical) variants of phrases; while there is no intrinsically 'right' spelling of a word, there is a sense (given what the constituent words mean) in which "I could care less" and "I couldn't care less" are objectively different, and the latter captures what is probably meant.
I mean to say that it is perfectly possible to insist on, and to try to enforce, a logical approach to the use of language. (Without this impulse, for example, we wouldn't have Lojban (https://en.wikipedia.org/wiki/Lojban)—which, OK, may not be a very practical loss, but I think we can agree would be an intellectual loss.) Granted this will not optimise for communication, or pleasant social interaction, but we all have the right to choose the fitness metric that we want to use!
The more you study language, the more you realize that none of it makes sense. It's a wonder how any of us English speakers understand what each other are talking about. I think the trick is to only look deep enough to gauge the sentiment of the presenter and no further. If you look too deeply, the whole thing falls to pieces.
The other thing that people often overlook, is that "could care less" and "couldn't care less" mean exactly the same thing IF the person saying "could care less" was intending to be sarcastic.
As in:
"I couldn't care less about this test." (literal)
"I could care less about this test." (sarcastic)
Yes, the actual expression is "couldn't care less" but I can easily see how people think it is "could care less" (in a sarcastic tone).
Same as "by the waist side" instead of "by the wayside." The term "wayside" is so rarely used now that people mishear it and rationalise the alternative definition that does make sense.
There are other examples too (correct on the right):
- Nip it in the butt vs. Nip it in the bud
- One in the same vs. One and the same
- You’ve got another thing coming vs. You’ve got another think coming
- Each one worse than the next vs. Each one worse than the last
- On accident vs. By accident
- For all intensive purposes vs. For all intents and purposes
Generally I agree with this approach, but this case seems similar (though obviously not in the safety aspects) to "flammable" versus "inflammable". Obviously you can't really stop actual usage, but I know this used to always confuse me when I was younger, so I'm disinclined to criticize people who yell "Stop!".
edit: Added clarification.