> That is incorrect usage though

We don't need no education

You wouldn't be here quoting that line if it were correct.

But pointing out that language rules aren't something that people strictly adhere to, with rigorous logic, is a useful observation.

Undoubtedly, but it was a response to someone explaining how to use English (correctly), not how to understand someone else using English (possibly incorrectly).

If I say 'proper nouns have a capital first letter' I don't think 'actually oliver sometimes people don't do that' is helpful.