[restalis]

Dictatorship (or totalitarianism, my preferred term for it) is not assured to be unstable. If done right, the totalitarian regimes manage to periodically weed out the internal threats, including dissidence, and thus keep the remaining masses content, a trick employed at least since the dawn of written history with Ancient Egyptian police[1]. As I see it, the totalitarian political system however, being one of the most rigid of all, is more prone to corruption than others. (You may think of the pun about power tending to corrupt and absolute dictatorial power - absolute corruption, but I'm more about the precarious ability to react to different form of corruption.) The communism's main idea is to please the majority, which happens to be the mass of mediocre, at the expense of the the ambitious minority, the needs of which are taking a back seat. This makes communism a lesser environment for development, but it's not in itself a destabilizing factor.

[1] http://www.reshafim.org.il/ad/egypt/law_and_order/police.htm