To the extent I am bothered by someone dissing a kind of music I like it is similar to someone saying my wife is ugly (that hasn't happened, but it would be hurtful if it had).So then why is there so much upset if someone says "avant garde music/hip hop/pop is garbage"? That's as valid a vote as any.
We have a personal stake in the music we find interesting, valuable, good. I consider it a form of rudeness for someone to go out of their way to call music worthless that they know someone likes. It is unnecessary and only designed to be unkind.
But it would not be hurtful to say, "I don't like avant-garde/ hip-hop music."