Politics and Capitalism isn't about what is best.
It is about diverting the will to power into something half useful.
In democratic capitalism, the easiest way to gain power is to either be elected (which requires convincing others that you have their best interests at heart) or figure out how to sell people stuff (which requires convincing others that what you sell them makes their lives better).
And when you gain power, you don't have to destroy the lives of those who came before.
In a dictatorship, to gain power you have to utterly destroy the existing social structure, and to defend your position you can brutally repress competators.
The goal isn't to be perfect or find the best solution. The goal is to make power-lusting people at least have to convincingly fake that they have the rest of our interests at heart. In societies that don't have that release valve, power-lusting people have to destroy society in order to gain the power they want.
The US Civil War is a wonderful example of the release valve failing -- the South, a power-lusting group, felt that it could no longer gain the power it lusted after in the framework of the USA. So it broke the union. The north felt that this violated it's own right to power, resulting in the civil war and mass destruction.
But that is a side arguement.
