Ah, but Polymath you're falling into a typical Western ideological trap when you say that the Soviet and Chinese models of communism weren't "pure communism". This is dangerously lurching towards the communism thread in the "Off-Topics" forum so I'll try to remain history-focused, but:
1. There is no such thing as "pure communism". How can any ideology ever attain "purity" in practice when you're dealing with humans? No theory can exist in purity; practical application is always the reality. Robert Owens' communes in the early 19th century failed, the Paris Commune failed, and the communist experiments of the 20th century have failed in spectacular fashion. Why? You blame it on a greedy few, but human ambition (in economy, society and politics) is a natural trait of our species, and while it has caused us much pain in our long history it has also brought us many benefits; what do you think got us into civilization in the first place? Communism was a magical, mystical theory that pretended it could make human ambition go away. Humans have done better with systems that have attempted to harness their ambition rather than suppress it.
2. The various communist regimes that have existed in the 20th century, in Russia, China, Hungary, Cuba, Cambodia, Ethiopia, etc. have all ended up as brutal dictatorships that have killed and spread poverty to far more humans than the supposedly evil Capitalism they were all railing against. This is no coincidence or mistake. These regimes are the natural outcome of communism as embodied by Marx, Lenin, Mao and Castro. Marx wrote that the masses would automatically realize their interests and organize, eventually rising up to overthrow their oppressors, the capitalist slave-drivers. Lenin realized that this was childish and would never happen, so he injected the need for a vanguard party to organize the masses - since they were clearly too stupid to see their own interests - and force communist paradise down their throats. Unfortunately, this would require a massive super-state and omnipotent dictatorship (an idea anathema to Marx) but added that this superstate would eventually wither away in Marxist fashion. But there was the little human ambition equation.... Creating massive super-states with no internal checks on their power simply gave some ambitious people an opportunity to take over and achieve power far above and beyond anything the worst robber-barons of the capitalist heyday could ever have imagined. It was a surprise to no one when Brezhnev conceded that the state had no intention of withering away, and was here to stay.
3. An oddity about communism, a theory created in the industrializing West, is that it never took root there. It found its expression in states on the verge of industrialization that were just beginning to enter the modernization process; Russia, China, Cambodia, Vietnam, Hungary, Cuba, etc. It began in states that didn't have yet the social conditions and classes (at least to the proportion that Marx discussed) Communism was designed for. Many of these states had to develop significant addendums to the theory to accomodate their own social and economic realities (for instance, Lenin's declaration that peasants were a "rural proletariat"). Pol Pot took this to an extreme and declared a sort of rural, anti-urban communism. Almost none of the communist leaders throughout the world actually belonged to the Proletariat; not Lenin, not Marx, not Mao, not Pot, etc. As a friend in Poland used to say, "Why are we listening about a theory for the workers when it's expounded by people like Lenin and Marx who've never worked an honest day in their lives? Did Marx know how to swing a sledgehammer?" In the West itself, few countries ever seriously came under the threat of a communist take over. Germany in 1918-19 might be the exception - and indeed Bavaria at one point briefly declared itself independent as a communist republic, but the modern industrial world has traditionally had small, weak native communist parties. Communists stood in and won some elections in France and Italy but usually by playing opposition to specific local policies and they were easily contained within the system.
4. So getting back to the original question posed on this thread; why do some who live comfortably and safely in the West expound communism even despite communism's historical record? I suspect guilt has something to do with it. Because of the Age of Imperialism and the subsequent world wars, it has become fashionable in the West to hold anti-Western beliefs. Communism suited that bill during the Cold War. It has less glimmer nowadays and therefore there are fewer adherants in the West than just a decade ago, but it was a neat and simple theory that claimed to solve all problems and blamed them on the West in the process (how convenient!) so it still catches the glint of some students' and academics' eyes...