Something is going on developmentally that requires progressive organization and changes in inner monitoring. The joys of infancy and childhood later require inhibition or repression, what Brenner calls calamities are the signal for change. We rarely find parents who were as restrictive as an adult's fantasy states. While repression was the first defense, displacement and isolation, among others, were introduced to explain other phenomena. They are differentiated from the top down, not the bottom up.
Defenses are the hows of conflict and compromise.
While we are trying to get rid of the homunculus in the machine, and a reified ego, I am not sure that the person provides a more satisfying agency. The developmental point of view suggests that only wishes that undergo later internal scrutiny are then rejected from expression. A psychology of compromise needs to account for the developing capacity to make judgments of unacceptability. This is not egoless. Similarly, primary process is a fiction.