Because without comprimise the world would always be argueing... and we would have destroyed ouselves years ago.
I believe the answer is: Regulate behavior
The self system is a concept that teach us to re-evaluate everything that we do in order to know their implications in the future.
By knowing this, we could determine the behaviours that would benefit or damage our development, which is really helpful to regulate our behavior.
Emulating unconscious biological functions is a function of the medulla.
