Oh, I completely understand that aspect of its use. I mean, Alucard pretty much says exactly that with his whole "only a human can kill a monster" speech. My gripe was more with the fact that the nail summoned plants in such a matter that alluded more to the crown of thorns. Simply put, I just think the artifact was handled poorly. The end is the same, regardless, and while I realize the nail was simply a means for Anderson to shed his humanity, I was still disappointed in the manner in which the nail effected him.