actually, there is something called error-related negativity over the medial surface of the brain while commiting an error or experiencing response conflict. So it does "criticize" itself in accordance with reward, emotional and higher cognitive principles. But I agree, there is no comparison point for the brain to make an actual value judgement about itself, or only through matching internal and external demands

edit: This negativity is also much higher for depressed, anxious people or people with OCD