Then how do you explain the success of Yelp, which is basically the same thing but for businesses? Or the school system, which is already designed around rating people? Or safeorscam, which was the same thing but for drug dealers? Or LinkedIn testimonials?
Certainly there are a ton of challenges to coming up with a good implementation — business, social, epistemelogical, etc. But I think the possibility space is too large to rule out the possibility of a feasible implementation.