The issue really has two separate, though related, parts. While congregations do draw exclusion boundaries by class, as you lay out here, there’s more to it. Congregations also draw inclusion boundaries that erase or ignore class identity. There’s usually an assumption the all of us identify as “people like us”. When someone does not — when, as you say, someone lives in a trailer, shops at Walmart, says “ain’t” — they know that they don’t meet the implicit class standard of the church. And because we in America don’t learn the language of class beyond the financial aspect, nobody has the words to discuss why some people inexplicably leave the church, nor to explain for themselves why they are leaving.