No. They know enough to understand that some people sometimes use words incorrectly and to work out what those people probably meant even if those people are saying the opposite of what they mean.
Saying "I could care less" when you mean "I couldn't care less" is objectively wrong. It's not, as you wrongly claim, subjectively wrong. It's as wrong as, for example, saying "It's raining heavily" when you mean "It isn't raining" or "<insert football team here> won 2-0" when you mean "<insert football team here> lost" or "water is denser than lead" when you mean "lead is denser than water". It's objectively wrong. The fact that many people can deduce what you probably meant despite what you said doesn't make what you said less wrong.
You're not ignorant. You're deliberately wrong for some reason.
While I sincerely appreciate your attempt to show me the error of my ways, I feel that you may be overthinking it.
In my opinion, I could care less is a long way from saying, it’s raining heavily, when it isn’t raining at all.
The “I could care less” thing is from the same stable as American-Yiddish inflections such as “I should be so lucky”, meaning “there’s no way that I’d ever be that lucky”, or “I should care” meaning “why should I care?” it’s a kind of veiled sarcasm.
In saying that, I realise that to lots of little Englanders anything American is infra dig.
Why use I could care less if we also have I couldn’t care less?
There are other pairs of phrases in English about which you could ask the same question.
Why say, “That will teach you to leave your car unlocked” when you really mean, “that will teach you not to leave your car unlocked?” or “You know squat about that” instead of “you don’t know squat about that.”
In addition, idioms don’t care about logic.
e.g. head over heels, shouldn’t it be heels over head?
As the famed linguist Arika Okrent M.A. Ph.D said, “People only use ‘I could care less’ to mean ‘I couldn’t care less’, never the opposite, it doesn’t cause legitimate confusion, although it does cause quite a bit of consternation, in any case, it’s here to stay.”
HTH