> they are discouraged at a young age by the school systems and parents who are worried that dialects like these are seen as "unintelligent" and will cause everything from bullying by children at school, to being turned down for interviews, jobs and even college.
I have two girls, and struggle with this.
At home, our language us is very different from when we're in public. I make it a point to correct my girls' grammar when outside the home (or when it's particularly egregious, like subject/verb disagreement), but generally don't at home. "I ain't gonna" is acceptable at home, but "I'm not going to" is expected elsewhere.
This approach is based on my own experiences.
On one hand, as an adult, I feel like I fit in well with the people around me even though I seem to have little in common with them - I'm a remote developer, and most of the people I interact with on a daily basis are tradesmen or other blue-collar workers. I'm convinced this is because I look, act, and sound like they do.
When I'm interacting with my colleagues I enunciate much more clearly and my grammar is significantly better, to the point that I sometimes wonder if my sentence structure makes me sound like I'm trying too hard. It seems to be effective.
On the other, I have a close family member who has struggled throughout her education with both grammar and spelling. She's a high school teacher now, but had to take her certification test numerous times due to repeatedly failing the language portion. She never learned to switch between colloquial and formal language, and never really developed a feel for what is correct grammar and what's not. She also has issues spelling many words. This could be because she is younger than I am and was taught using a different method (she learned "sight words" first; I learned phonics), or it could be because I read a lot more in childhood than she did.
At the end of the day, I want my children to be able to speak at the same level as their professional peers, and I want their peers to be educated professionals. I also want them to be able to self-identify with the people they grew up with, and not to immediately associate a dialect of any sort with intelligence.