There is an intractable problem faced by all systems of rule, be they democratic, socialist, or fascist: humans abuse control.
As long as people are involved in determining policies, the fact remains that humans enjoy rewarding friends and punishing enemies.
Give power to a group, and they subjugate the minorities to expand their power.
A constitution actually doesn’t solve this problem, they can simply use the power to make the constitution irrelevant unless it suits their views.
Checks and balances only work when there is a conflict of power. If all agree to expand the reign of rule, what is just and true doesn’t matter.
It is not possible to inject sense into a violent institution.