As a kid in the 50's & 60's I too was ashamed of speaking like a Brummie, or in any accent for that matter, but these days no one should be ashamed of their accent. On the contrary you should be proud of any accent that you speak.
When I first moved to Flanders in the late 60's people here all used dialect, it was so (bad?) that every village and town had it's own dialect. In some parts dialects varied from street to street, or even in the same street! This was, in those days, because most Flemish people didn't move about anymore than was needed, a lot of them still don't. For most of them going to another town or city was just not on, why should they? That was their way of thinking. I can imagine that life in England some 100 years or more ago was the same way.
After my first heart op last year, I came in touch with a 70 year old Flemish farmer that was also in for a heart operation. Through moving around all over Flanders to ride bike races I have become quite an expert in dialects, but this farmer used a dialect that I had never heard before. After a few days I began to understand what he was saying, my skill was so great that the nurses asked me to translate between them and him every time they came to nurse him! The farmer told me that in all his life he had never been further than outskirts of his farm, his visit to the hospital was the first time in 70 years that he had been out of the farm gate. Then and only then did I discover how dialects and accents come about. People in a community, be it large or very small, as in this farmers case, develop their own language or dialect. It is for them enough that they understand each other, no need to understand other people as they never travel out of their area. I am no professional but I can pinpoint where someone is from in Flanders.
Luckily we don't have class barriers in Flanders so no one trys to talk posh all the time, as you still get a lot of in England. I always say "if you're not born to the manor, why try and pretend you're something you're not?" That is down right snobbery.
There were attempts to level out the language here in Flanders, but luckily that died a death and now the dialects are being recorded to save them for future generations.
This is getting a bit long so I'll stop here, I have more to say about Brummies and I'll do that soon.
Graham.