I'll bite: I couldn't care less about anyones irk's - You get the point of what he was trying to say .... so why point out the difference? - I think its a smug ass hole thing to do.
I upvoted you because it is a smug, asinine thing to do, but I disagree with your implication that he thus should not have done it. However, because this is One Of Those Issues, I have split my reply into two conceptual sections:
Objective:
It seems that the world is largely organized into two classes of people: those who care about precision of speech beyond the simple need for making someone else understand your point, and those who believe that as long as everyone is on the same page, then for God's sake, it bears no further discussion. "I could care less" apologists are in the latter group, clearly, but it is important for both groups to exist and speak up. Of course, this means that while I disagree that he shouldn't have mentioned it, I agree that you should have criticised him for mentioning it.
Subjective:
My disgust with "I could care less" goes beyond mere imprecision of speech. There are people in this HN thread claiming that when someone says "I could care less," they mean "I could care less, but it would require effort." I think that this is definitely not what most people think they are saying when they say "I could care less." I think most people are trying to express, "I couldn't care less even if I tried," but are failing to express that because they are simply regurgitating things they have already heard. This is a pernicious habit indicative of a deeper lack of thoughtfulness and creativity in our society, and it drives me completely crazy.
I agree with you in broad lines but would like to raise one nuance that I find essential to the ongoing debate.
Many now popular constructs in contemporary language have come forth from – at their time – seemingly illogical mutations. By banning all seemingly illogical new ways of saying things, or in other words: only letting new constructs that make more sense pass unopposed, we effectively kill a language. A language that allows for only the most logical and most effective of ways to express ideas has no room for creativity. (I'm referring to creativity with the language, as in playing with the language, e.g. stand up comedy or creative writing; it is perfectly possible to be creative using a dead language, or to write beautiful – syntactically correct – code.)
Considering how evolution seems to work, such a 'pure' language is inevitably where we'll end up if we kill off all seemingly illogical new constructs.
To bring my point back to where I started: There are not two groups, one that cares about precision of speech and one that doesn't. I understand you deliberately simplified your explanation, there are never 'two groups', but I think there's another, more interesting, way to view this difference beyond just stating that there obviously must be a continuum between two extremes. I pose that we all have a certain tolerance level for how incorrect a construct may be with regard to how we value its addition to the language (is it merely a lame bastardization, like "I could care less", or does it have actual merit, like "to upvote") for us to accept or reject that construct.
If we shoot down "I could care less" only because it's unsound – or if you prefer, incorrect or imprecise – we may be smug, but we are definitely being reckless and are doing the language a big disfavor. If, instead, we point at this wart in someone's copy because its (1) unsound and (2) lacks any merit over the correct version, I don't think that's smug, let alone asinine, at all.
I don't point this out to people for the reason stated. It does irk me, but I keep my peace, even when it's my own brother.
That being said, this is a forum that is detailed and critical by nature, I don't feel it's smug to voice a subjective opinion on the matter.
Still, you're right, it can be(and most likely is in most situations), a very rude and smug thing to do, but it all depends on the person as well. Do they receive critical comments well? Will they be enlightened because of it?
"Richard Feynman, [Murray] Gell-Mann's chief competitor for the title of the World's Smartest Man but a stranger to pretension, once encountered Gell-Mann in the hall outside their offices at Caltech and asked him where he had been on a recent trip; 'Moon-TRAY-ALGH!' Gell-Mann responded in a French accent so thick that he sounded as if he were strangling. Feynman - who, like Gell-Mann, was born in New York City - had no idea what he was talking about. 'Don't you think,' he asked Gell-Mann, when at length he had ascertained that Gell-Mann was saying 'Montreal,' 'that the purpose of language is communication?'"
A fine anecdote - Gell-Mann was of course communicating not only that he had been to Montreal, but also that it was a French name, that he new the [approximate] pronunciation and that he anticipated Feynman to be equal learne\d.
edit: This comment also puts me in that category.