Proving that anyone can carry a crazy idea around in their heads.
It isn't really crazy, I myself think that life is probably common throughout the universe but I have doubts about there being much intelligent life if there is any at all. I also have questions about why intelligent aliens would come here and not interact with us in some meaningful way.
The fact is that there is nothing here on earth that is special. Any resource aliens could possibly want can be found in great abundance throughout the universe. If they can come to earth they can get the resources with ease closer to home. That leave animal and plant protein as the one resource they may want from earth.