I would say that over a long enough period of time it's unavoidable that a selfish person will use the power to gain more. Selfish people are more likely to seek positions of power, so even if most people are altruistic, the people that seek power are more likely to be selfish.

I’ve come to basically the same conclusion. Attempts to engineer perfect political systems that are immune to this sort of infiltration is like trying to build a structure that will never need to be repaired—you can expend a lot of resources and effort on it upfront, but on a long enough timeline there will be failure modes you didn’t foresee.

Then how do you explain that all attempts at communism ended in dictatorships, except (perhaps) Israel, whereas the list of capitalist republics that ended in dictatorship is pretty short?

Oh and how do you intend to solve that most "communists" leaders were fake and intended to become dictators from the very start. There's many cases of various dictators, from anarchist, to just self-interested people, fascists, religious lunatics, ... pretending to be communists to grab power. In many cases, communists supported these awful people with extremely bad results. Examples: Russia, Afghanistan, Iran, Poland, Venezuela, ... all are cases of communists supporting would-be dictators that had ZERO intention of ever making those societies equal or tolerant or democratic.

In fact there's plenty of people who got support by pretending to be communists, even going so far as committing terrorist attacks on behalf of communism, to turn around and become capitalist "leaders", like ... well, most of the members of the EU commission for example. Jose Manuel Barosso, for example, was part of communist protests that lynched people. He was also the EU commission president that pushed Greece into debt servitude.

In other words, cancer always spreads.

Not necessarily the first cancer, but eventually one will.

Cancer is when a component of a system acts to replicate or enrich itself instead of acting to perpetuate the system.

Cancer can be also said to be fault of a system living longer than it needs to. In the end, what matters less is the specific instance of the system than ensuring the continuity of development is passed on.

But for states, they still feverishly cling to the idea of unity even as it brings increasing fragility and stagnation.