Board Thread:Speculation House/@comment-4830106-20131108040231/@comment-10390252-20140211165151

During her exposition on Aura, Pyrrha put across a strong implication that the Grimm aren't "alive" in the strictest sense of the word, both in her comment about them lacking souls and also her comment about them being "anonymity". So, the idea that they are in some way artificial (maybe the golem-like creation of some kind of dark power) is not unthinkable.

Remember: In LoTR, the Uruks were mass-produced genetically-engineered super-soldiers in a magical/fantasy setting. So it isn't impossible that something might use the power that seems to be everywhere in the RWBY universe to mass-produce foot soldiers to destroy humans for some reason.