What does the fact that punk was made by working-class kids have to do with the music?
Except by no means was all punk made by working class kids.
Here's a question. How come hip post-modernism gets as far as crap like viewing everything ironically, debunking the cult of the artist, embracing pop as a worthwhile artform and whatnot, but doesn't take the fundamental modernist/post-modernist idea that a text is independent of its author.
All this focus on the race and class and gender and so forth of the artist (as if it actually matters as long as the music's good) actually does is lead to ridiculous crap like black rappers being instantly more credible than white rappers, and those old classic crap comments on pitchfork and whatnot about 'white guys with guitars' (as if every band fitting that sort of demographic is somehow identical). The only circumstances that I personally find this sort of thing to be important in is if the band makes it a central part of their music: for example, I will ridicule Good Charlotte for singing about how they don't like rich people, because they're rich pop stars, whilst I will not ridicule Skyclad for singing about how poor and hungry they are on their early albums, because they were.
It's not that I don't think it can be a concern, especially if you're talking about history of music and whatnot, but I think it's generally just taken too far.