Capitalism did its job like democracy, but both are systems that fail and will fail. The current alternatives are far from any better.

The best system that can be maintained indefinitely will be a form of socialism, where constant growth is not the goal, but balance and stability (leading to equal standard of living for all). However this cannot occur in a transition period, simply because the rate at which humanity has evolved technologically is unprecedented. At this rate any system will fail since they have to change drastically to fit a new society.

Together with that, human have not evolved spiritually at all, we are the same people that traded slaves, started world wars and all the genocides in human history. We simply do not poses the spiritual tools to design a better system despite our technology. Even if we do it, it will fail because of our nature.

The closest we can get to a system that is sustainable is to have the mentality of the Japanese culture and the goals of a socialist system. But we are too diverse for that in this world. There is a reason why the Japanese are where they are today after so much destruction in their history. It's all about realising that we are all a part of the same being, which too many forget in their selfish life.