I don't really see how this would differ from giving a person points. Posts are not anonymous after all.
Then again, everyone may just ignore the scores if they object anyway. It's not like there are any actual consequences ;)
it differs because a "person points" are immediately visible and whereas they should be used to give someone an overall "rating" it is in most case abused, and people tend to battle over who has the best rep and this gives moderator more work .... (not even considering how partial it is to try to give a single rating to apprehend someone's value)
on the other hand, a "per post score" (with nothing kept in the user profile) only means something on a single post, while it can be abused, any kind of abuse is mitigated by its very small scale, only people reading this particular post will see the "score".