So I copy someone's music, publish it under my name, and then say "Nobody seems to be complaining that it's bad music. What's the problem?"

First, people listen to absolute garbage. General taste is not a standard. Second, the quality of the music doesn't make other problems magically disappear. This music is built on enormous amounts of other people's music, and at the same time threatens to almost completely undermine music making, from amateur to megastar. That's a problem.