its underlying assumption that nobody is ever motivated by anything other than pure self-interest and/or greed.

That's a really good point.

I think the problem with the RIAA claiming to represent the artists whose IP is being appropriated is that many/most artists/musicians aren't driven to create by greed.

And so is that.

As an artist myself I totally agree with you. One step further is that the music I create is spiritual in nature and my conviction is that I do it not for the money but that other people might be spiritually blessed. So while I hope to make money someday to support my "ministry", it is certainly not the overriding factor.

So my own situation puts a big fat hole in my theory of IP protection being necessary for music to be created. However, it's still true that a lot of music we have wouldn't have been created if someone hadn't gotten money for it, if for no other reason than to put food on the table while the person makes the music.