Very true - which is why I don't think communism can succeed any more than capitalism - or feudalism - or hunter & gatheringism ....etc. Over time, those with a heavy dose of greed for wealth and power will work/mold the system to their favor until enough people get angry and rebel - then we start again.
Of course feudalism is based on greed and power, it's not something that was corrupted that is just exactly what it was, the more vassals you had the better off in general you were. It was always a way of concentrating capital to the top of society.
Hunter/Gatherer society structure was just something that disappeared (for the most part) with the improvement of agriculture, no one ever rebelled against it.
Communism has never ever really been implemented as Marx saw it, as a system naturally arising from the people rather than a top down implementation (plus whatever was implemented in the USSR and China was never communism).
Capitalism I don't really see much better and I don't agree on what many people see as an inherent link between it and democracy.