[Whit]

     So, any fertilizer used has to come from non-human animals? Damn, not even our crap is natural...

     Jokes aside the idea is that humans violate nature. Thus are unnatural. I really think Steve and Bruce nailed it. To give an example, I've heard people argue that homsexuality is unnatural because it's unique to humans. When I pointed out that was absolutely false, even pointed out that a dog on a leg is cross-species as well as often same gender I was told that was due to human influence. Go figure.For the record I did bring up other animals, such as rats, and was told that was scientists just finding what they wanted to. Again, go figure.
     End of the day, I agree it's just a cop-out.