If you don't have intuitive experience with using different forms of language in different circumstances, it means that you're part of the privileged group that gets to make their dialect or language the standard.
Sure. I can agree with that.
But you're changing the argument here. You were originally arguing that the Standard English used to write reports at school, compose documents at work, and write resumes was somehow different from the language that is used while talking to family and friends. My point was that this is incorrect. Standard English is appropriate in all places English is used.
Non-standard dialects (of any kind) are not.
I know you don't mean to be picking on people, but calling someone's dialect "incorrect" is not fair.
I'm not sure where fairness comes into things. They're 'incorrect' from the perspective of being deviations from standard English and (as we've established) inappropriate for non-casual usage. Complaining about unfairness in this situation seems like complaining about gravity pulling my feet downward and preventing me from flying around.
Laughing at them even more so. It's unfortunate that people from Newfoundland have to learn to speak perfect Standard Canadian English just to be taken seriously.
They don't.
The guy who taught us aerodynamics was well liked and respected. But the first impression with the thick accent and heavy use of colloquialisms was usually laughter due to difficulty in understanding. This occurred because he
didn't learn very good Standard English, instead forcing others to deal with his dialect. (He did write his textbooks in perfect Standard English with no colloquialisms.)
A dialect is essentially a separate language that just hasn't diverged much yet from the dialect considered standard. It has its own rules separate from the standard dialect, and it's tied closely to the identity of the people that speak it.
I like the concept of a dialect as a different language, and it makes sense to me and is a good way of thinking about them. Many languages are closely tied to the identity of the people who speak them.
As an English speaker, it would be weird of me to go to Thailand and expect easy communication / work / concessions while speaking English. The correct thing for me to do would be to learn standard Thai if I was expecting to conduct my business/education there. I'd keep speaking English of course, but that would largely be relegated to the occasions when I was with other English speaking people. To speak English in a setting where Thai is expected would, of course, be incorrect.
Calling a dialect "incorrect" is just a mild form of the same culture that thought indigenous Canadians would be better off speaking only English.
I don't think I'd ever argue that speaking only one language is for the best. Languages help a persons mind develop in a variety of different, beneficial ways. Languages themselves expose a person to wider cultural differences and ways of thinking. Learning more languages is better in pretty much all the cases I can think of.
The white Christians who thought that indigenous Canadians would be better off speaking only English didn't care at all about the English language. They were very clear about their goals - to eradicate native religion and culture to enforce dependence so that they could be controlled more easily. The Canadian government (assisted by Christian churches) went out of their way to build some very specific and horrific ways of going about doing that with impacts that have damaged native communities to this day. The goal didn't have anything to do with correct usage of the English language, or dialects . . . and it's a little odd to see you somehow try to equate the two.