[StavrosK]

There are two ways to look at this: What the words actually communicate, and what you know them to mean. If you told an alien "I could care less", they would have very little information as to your state of caring. Therefore, the phrase fails in that respect.

If, on the other hand, you treat it as a nonsensical synonym for "I don't care", then the phrase would well have been "gooble gooble goo" and it would make no difference, since everyone knows what you mean when you say it.

I find arguing its correctness moot because there's no way to spin the sentence to be correct. At most, you can say "well, you got the point", and that's the end of it, at least when you're dealing with a descriptivist (which you aren't, in this case).