Greedy sociopaths are a fact of humanity, they will always exist and will always be drawn to positions of power. The fitness of any system to avoid authoritarianism is based solely upon the effectiveness of the obstacles it erects to oppose aspiring dictators.

Materialism isn't just about base economic principles, it's about ensuring that your systems are suitable to actual reality, rather than just utopian hypotheticals. Anyone can design an idealistic democratic system of government that works perfectly when everyone is kind, reasonable, and cooperative, but such a system is useless. Lasting success requires a system which fulfills the necessities of government efficiently without being exploitable by greedy sociopaths.