Some people are just evil. While this term is a relative one according to moral relativists on the left these days, there are those of us for whom institutionalized mass murder still qualifies. Many on the left simply love to puke the rhetoric that people died and were oppressed during America's ascendancy too. To this, I would answer that there is no comparison between the moral shortcomings of a nation that was evolving  over its 250-year history, and individuals who were able to rack up millions of victims over a mere few decades. 

It is estimated that Communism has resulted in the deaths of around 100 million people worldwide; this is not counting the communistic socialist nations that did not overtly embrace the philosophy of Karl Marx. Given the dumbing-down that has occurred over the last 40 years, many Americans aren't even aware why some of the iconic leftist leaders my generation grew up learning about were evil, and why anyone who holds admiration for such excreta is either profoundly deluded, grotesquely stupid, or a seditious traitor who ought to be suspect - at the very least.

Killed - Mao killed 20,000,000 (that's twenty million) of his countrymen in pursuit of his grandiose communistic ideal. This isn't counting those who starved to death as a result of his policies. I guess he was concerned about population control...

Killed - To be determined; Castro's regime still holds power under his brother Raśl. Tens of thousands died in the weeks after Fidel's ascent to power. It is estimated that Castro has killed over 100,000 people. This is difficult to determine, however; it's not like the Cuban government is going to release relevant statistics to the Western press.

Killed - Since Che was never the titular head of a nation, he didn't actually get the opportunity to initiate systematic murder as did Mao or Fidel. He was party to the deaths of the 100,000 or so people killed during the Cuban Revolution, however, and countless others that remain undocumented.

Killed - Lenin and his henchman (and fellow revolutionary) Leon Trotsky were responsible for killing between 4 and 5 million Russians during and after the Revolution. Lenin later had Trotsky assassinated. Notice a pattern?

Killed - Outdoing Lenin and Trotsky, during his purges, Stalin was responsible for the deaths of approximately 60 million Russians, Russian and Eastern European Jews. While communists love to point to Nazi dictator Adolf Hitler's atrocities (which were admittedly heinous), Stalin's paranoia and pogroms of murder are nearly universally overlooked by his fans and the modern Western press.

Killed - To be determined. Typically, he gets others to do his dirty work.