What do you think is responsible for turning mainstream rock into the sad lifeless thing it is today?

Many people say it was grunge, others say it was nu-metal, still others say it began during the hairmetal era when style first started to noticeably dominate over substance. I believe it began in the 70's, with a little movement called punk. 3 chords and singers who can't sing to save their lives - now a common sight in modern rock - began with punk. Grunge made it huge in the US, and now we have to put up with garbage like metalcore, emo, screamo, and God knows what else they're calling it (all of it sounds the same anyway). Granted, punk did aid in the creation of thrash and speed metal, and it gave us great bands like the Clash and the Misfits...but it's positives are far outweighed by it's horrible impact on rock as a genre. These are my thoughts, I'm interested in what you guys think.