That's a good point, but I'm pretty sure (although I would have to double-check) that YouTube (and similar sites) has an agreement with the major record labels to cover that.
Regardless, one can differentiate music videos, which are still viewed primarily as promotional tools to move albums and singles, from products which are intended to be the final end use, such as a documetnary. To put it another way, you won't see me downloading music illegally, but, as a former musician, I do view videos differently, because they are created not to be sold (unless as part of a compilation), but to be watched in order to encourage people to buy the album, or the song.
There is a difference between uploading a small segment of something (and a video is just one song from an album), and uploading the entire enchilada, i.e. a documentary.
If, for example, someone wanted to upload a clip of one of my films, and then provide a link to where the film could be purchased, I would have no problem with that. But by uploading the entire film, you are directly competing with the producers, even though you aren't selling it. That's something I do have a problem with, although not in the case of Aztec 1948, for reasons I stated at my blog.
In other words, a music video is like a promo clip from an album. I don't think you would find any musicians who would have a problem with it being uploaded and watched as much as possible. However, if one were to object, I would expect YouTube to remove the content from their site; I would certainly remove it from mine.
Best regards,
Paul