I'm not the poster you quoted, but I guess I don't "get" your point either. I'm not trying to be obtuse. I don't think anyone is disputing that saying "sir" and "ma'am" to everyone is a southern thing. The dispute is coming over whether saying "sir" or "ma'am" indicates good manners (and lack of saying so indicates poor manners), or whether it's just "a thing".
In your anecdote (which is cute), you say:
But, then in your "geez, people, it was just a joke. Of course you don't have good manners when throwing a tantrum" response, you seem to indicate that she says "sir" or "ma'am" whether she's using good manners or not. So, in that case, it seems to lean more to the side of it's just "a thing southerners say," not actually good manners.
Were you being facetious in your first post (that doesn't read very well in text)? I saw the little rolling smiley face, but I originally took that as "isn't my daughter adorable" rather than "isn't that ridiculous that she says it even when using bad manners?"
In addition, regarding a previous poster who was shocked by the poor manners of her daughter's friend who didn't say "ma'am?" when she hadn't heard the question ("ma'am" was "the correct answer," according to that poster.) I agree that "huh?" or "what?" probably wasn't the most polite response. However, I don't see "ma'am?" as being any more polite than any number of other possibilities that don't include "ma'am." ("Pardon me?" "Excuse me?" "I'm sorry, Mrs. Smith, I didn't hear what you said..." etc.) If someone responded "Ma'am" to me in that situation, I would probably have been confused because I would have assumed that "ma'am" was their answer to my question, rather than a request for me to repeat myself.
Not to beat a dead horse, but "ma'am/sir" definitely seems to be a southern thing, but I think some of us are frustrated by southerners patting themselves on the back for their superior manners because they say "sir/ma'am" and other people don't. It can definitely be part of good manners, but just because someone says "sir/ma'am" doesn't mean they have good manners or that their manners are better than another person's.