I guess I'm still confused. I pretty much register all of my copyrights (13 so far) with the LOC. I'm not worried about anyone stealing anything, in fact that would be really nice if they "stole" my music or words and actually got a hit published. I would be set.
The problem is that if an author places their work in the public domain, they irrevocably give up all rights to that work. This site's policy is that any music placed here is placed into the public domain. Therein lies the problem.
Rock on!