I understand that perhaps you haven't included this option because other users are allowed to use songs that one uploads. However, a user should still be able to delete songs they have uploaded. Perhaps they accidentally uploaded a poor version of a song, or maybe they just decided don't want the song available to anybody else anymore (especially if it's an original recording), or maybe they want to quit using your site altogether and delete all of their mixes. If you wanted to dissuade them from deleting a song, perhaps you could offer a warning if the song is in somebody else's mix. But the option to delete a song should still be available to the user who was the original uploader; it's only fair.