I think that, as with all prejudices, it is O.K. as long as you are aware of them. I know that I have been guilty of inverted snobbery in the past because I assumed I was not going to like someone who had been to public school or spoke with a plum in their mouth. Ian Hislop has converted me!
I now accept that people speak they way they were brought up to speak, and it doesn't tell me anything about them as personalities.
I can't say that my Salford accent, now much diminished as I haven't lived there for over 50 years, has held me back in my career. I think it is easy to blame other people's prejudices for your own failings - 'I didn't get the job because I am black, a woman, disabled, not posh enough, too posh.....' No doubt these complaints are often true but sometimes people don't get jobs because they are just not the right candidate for that particular job.