I see your point, and to an extent I agree. But when that locally accepted change in the language reverses the meaning of the (e.g. I could care less vs I couldn't care less) I feel it begins to limit the ability of speakers of that dialect to communicate effectively outside of their group...

Look up the etymology of "revolution".

So there is a need for a universal version of the language for inter-group communication. Then we can also have local dialects full of loan words, slang, locally specific similes,... that are more expressive and beautiful than the universal version.

Yeah nah, you're being a complete dag.

Famously English never cleaves the meaning of a word to cleave to its opposite meaning.

it really doesn't, no one has ever struggled to understand that phrase. I'm autistic and though my brain didn't like the logical inconsistency I could understand what was being said. every language has weird quirky idioms, it's not a big deal

See there's your lede: if it makes communication more difficult, THAT'S when it's "worse." That I can agree with.

"I couldn't care less" is perfectly fine, because everyone knows what it means. Language is not a math problem; fixed expressions are not the sum of their parts. "I couldn't care less" is no more incomprehensible or invalid than "kicked the bucket."