critic [ˈkrɪtɪk]
n
1. a person who judges something
2. (Literary & Literary Critical Terms) a professional judge of art, music, literature, etc.
http://www.thefreedictionary.com/critic
Music critics like performers are subject to criticism from their readers and employers. If they get it wrong I have no doubt that will be made clear to them.
To reduce the commentary upon music to mechanistic objective guidelines seems to miss the very essence of music which is it's necessarily subjective power to move people emotionally.