Good question–it’s a gray area even in terms of my personal sense of right and wrong with the links to the specific mp3s I publish.
But, basically, there are commercial sites that hotlink to my CC-BY-NC mp3 files, and don’t link to any pages on my site otherwise. And, it’s clear that the intention of these sites is to use aggregate music in a bulk fashion to attract traffic to view commercial ads to generate revenue for the site owner.
There’s no obvious intent to highlight my music or present it in a curated context, and neither does there seem to be any intent in serving a public good by simply being inclusive or comprehensive.
I don’t consider this (and don’t think it is) any kind of legal violation of the CC license–these aren’t “uses” / they’re just links. But, they’re links created only in the technical and robotic sense–and not as any kind of expression of artistic or even pragmatic human desires.
So, these links are lame, and that’s kind-of undesirable.
That said, whenever someone listens to a track on one of these sites, that individual is bringing humanness back into the mix. IMHO, morally and artistically, this may cancel-out the lameness that created the play-button that the man or woman is pressing to create music. But, that lameness is still kind-of yucky.