As a musician and songwriter I've thought a lot about whether rock music is valid and I believe the question has a complicated answer.
First: ALL commercial music including rock has become (some would say always has been) part of the lifestyle industry which sells products from alcohol to vacations to zit cream. Anyone who thinks they're part of some sort of cultural revolution when they play a hit song by a mainstream commercial artist is deluding themselves. You're being manipulated plain and simple.
Second: If you've been to a dance lately you know that rock and roll as music to groove to is just as fun and popular as it ever was. "Single Ladies" might get the biggest cheer today but "Spirit in the Sky" hasn't lost its ability to pack the floor every time. When you're putting a set list together it's always safest to stay away from pop trends (see Cotton Eyed Joe) and stick with Alan Jackson and AC/DC.
Third: Rock music is at its core guitar music so the question could be: is guitar - and especially electric guitar - still an instrument that a musician can use to express himself as powerfully as he might have in the 1960s and 70s? I can only speak for myself when I say that the guitar is as exciting to me now as it was when I first plugged in over thirty years ago. And judging by my guitar students the interest in guitar is waxing not waning.
Finally: Todd Rundgren said in the 90s that we are in the age of "retexturization", a phrase that resonated with me and seems to describe modern music perfectly. Computers allow musicians to incorporate hundreds of styles and sounds into their unique vision. A bluesy back beat or a power chord have become part of the language that an artist can use to tell a story or evoke a feeling (see Beck). I don't think rock music is any less valid a part of the musical language than pop, jazz or classical is. It evokes the raw, the primal, the sexual as powerfully now as it did when Elvis brought it to life.
So I say, rock on.