Ooh -here’s an interesting link I haven’t seen before; this site also gives four reasons that the ‘could’ phrase is respectable, and they are slightly different to my list.
The first one is intriguing;
I have sometimes wondered if this phrase is influenced by American Yiddish phraseology; even if not it might sound familiar enough to some speakers to resonate in the same way.
Must be an echo in here.
You’re a day late and a dollar short, my friend. I already shot that one down.
I have reviewed the thread, and see no evidence of that. In which post did you make this rebuttal?
Not sure there’s a good answer to that question. Hitting “reply” in response to a link is not what “shot that one down” means, not even idiomatically.
Another link to someone who has seen the light; the ‘recovering nitpicker’ Jan Freeman
http://www.boston.com/bostonglobe/ideas/articles/2010/10/24/i_could_care_less/
She mentions William Safire’s premature comment (in 1979) in his New York Times column that “could care less” had finally run its course: “Like most vogue phrases, it wore out its welcome.”
So it was a ‘vogue phrase’ in 1979? That sounds suspiciously like a lot of hipster-types using it consciously, with (dare I say it) a certain amount of irony or sarcasm.
Apparently not very thoroughly:
http://boards.straightdope.com/sdmb/showpost.php?p=17689229&postcount=235
Also, I will point out that the part of the article you quoted ADMITS that “could care less” didn’t necessarily originate with sarcastic intent. Isn’t that precisely what we’re arguing about?
Ah; you state that you don’t hear a sarcastic tone, which makes it different to the Yiddish phrases you reference. That may be the case today, but some posters (and Pinker) have described such a sarcastic tone as existing in the past.
I suspect there are several different types of use for this particular idiom, which might be muddying the waters. There are some users of this phrase who do use it ironically or sarcastically, as Pinker seemed to have detected back in 1994, and panache45 claims to remember personally.
There are other users who claim to detect an ellipsis, a missing but implied part of the phrase which acts as a negative (*As if *I could care less is one particularly convincing example).
Others simply point out that the phrase has never been used in its literal sense, but only with an implied negative.
Finally there are no doubt a large group of people who never think about the meaning of the phrase at all; these seem to be the people that most prescriptivists are concerned about, and probably with some justification. But they are not the only users of this phrase.
Hmmm… you are quoting, in the same thread, a source claiming the phrase had a sarcastic tone in the past and morphed into one without a sarcastic tone, and earlier in this thread, a source claiming it may not have started out as sarcasm, but morphed INTO sarcasm. When you cite two different sources that pretty much directly contradict each other, I am not convinced.
What you’re saying, then, is that these so-called “authoritative” sources you are relying on are really all over the place, and amount to nothing more than people taking wild guesses in defense of an idiom that makes no sense.
I never said it was used literally. What’s your point?
Well, I thank you for at least acknowledging that. It’s certainly less stubborn of you than the others in this thread.
John Cleese weighs in:
These unthinking users are no better or worse than the people who describe themselves as head over heels, who never think of the literal meaning.
And ‘could care less’ still sounds better…
By the way, let me elaborate on this. The part you quoted says “could care less” has “staying power” NOW, because it “matches up well enough” with phrases that use Yiddish inflection. But here is someone using the phrase (about 28 seconds into the video):
It sounds NOTHING AT ALL like Yiddish inflection. It just seems to me that people, in defense of this nonsensical idiom, are grasping at straws to try to explain why it would make any sort of sense.Here’s another one, just to show you how thoughtlessly this phrase gets thrown around:
Tom Brady says, "Truthfully, I could care less about watching the game."Not only is there no inflection in his voice that would imply he’s attempting to be ironic, but he sounds dead serious, and even adds the word “truthfully”, which makes the phrase even MORE nonsensical, and removes even the slightest glimmer of hope that it could somehow be interpreted as being ironic. It’s beyond obvious that he is merely repeating the phrase as he knows it, without the slightest regard to what the individual words mean.
Actually, yes, I know what a dictionary is. The electronic version of the OED that I mentioned was given to me by a colleague at the University of Waterloo – just down the highway from here – who was then engaged in the historic New Oxford English Dictionary project – and he explained to me what it was. 
Seriously, though, you need to ask yourself whether a dictionary is primarily a record of usage or whether it’s a prescription for usage. The distinction may seem a pedantic one, but let me illustrate. Suppose we are trying to decide what word to use to express a certain concept. We have one word that has, let us say, 39 different meanings, of which one rarely used one carries that meaning, but the word almost always means something quite different. Then we have another word we could use which is almost always used to convey the meaning we want. Which one – in the general case – would be preferable? This should also explain my understanding of “preferred usage”.
Once more: the number of definitions has nothing whatsoever to do with which term is preferable. The preferable term is the one that successfully conveys the subtleties of meaning intended by the speaker to the audience. Full stop.
In this case, “I’m well” conveys a very slightly different meaning from “I’m good.” The latter phrase is, to my ears, slightly more informal sounding, consequently implying a more relaxed relationship between speaker and audience. It’s a small difference, but it’s there.
In any case, you’ve moved from objecting to “could care less” for unsound reasons, to objecting to “I’m good” because it puts an adjective where an adverb belongs, to objecting to “I’m good” because even though a dictionary definition supports its use, not enough dictionary definitions support its use. Isn’t it time to take a step back and ask yourself if you really want to defend this hill?
Even if this idiom emerged as a mistake (which has certainly not been established) it apparently became a vogue phrase some time before 1979; I can easily understand why some of those who used it in those days applied a sarcastic or ironic intonation. Nowadays it has become more accepted, so it appears to have lost its intonation, if it had any.
Liberman has analysed some voice data and found some differences in intonation between the versions, but not necessarily ones he can attribute to sarcasm; the phrase is just easier to say, so has a different rhythm.
Nevertheless the ‘could’ phrase is just as logical as ‘head over heels’ so it is arbitrary to accept one and reject the other, except that ‘could care less’ has emerged comparatively recently.
Well, yes, affecting your audience’s dialect is always good for relationship-building. Politicians try to do this all the time. The same claim could be made about “ain’t” and “y’all”.
But there is no sense in which the meaning is “slightly different”. The meaning is either completely different, if one takes the common definitions of these adjectives, or it is exactly the same, if one interprets it colloquially. The fact that there is an obscure sense in which “good” is allowed to mean “well” does not dissuade me from thinking, every time I hear “I’m good”, that the person is either on the straight and narrow path to salvation (or at least in good standing on Santa’s list) or else possesses some notable skill. 
No, the key difference is that “head over heels” is an inversion of a metaphor, while “could care less” is an inversion of a literal expression. It’s exactly like saying “I believe it” when you actually mean “I don’t believe it”. It’s not just completely different, it’s rather uniquely bizarre.
Well, it’s not completely unique. There’s “I could give a damn/shit/fuck.” I’m assuming that’s influenced by “I could care less,” but I don’t know.