Communism killed tens of millions due to the forced collectivization of production. That happened in the USSR, China and Cambodia. Today, North Korea cannot feed itself whereas South Korea has emerged as a vibrant and wealthy economy.
While conceding that force collectivization is generally a bad idea, blaming it for human rights violations is a bit disingenous- in all three of those countries, there had been years of war that had desensitized them. China, for instance, had been in a nearly constant state of internal warfare and external invasion since 1911, when the Manchy Dynasty fell.
I should also point out that China had very bloody civil wars during the Taiping Rebellion of the 19th Century (20-100 million) fall of the Ming Dynasty in the 16th century (25 million) or the fall of the Yuan dynasty (20 million).
But, yeah, they would have killed each other over communism if they knew about it back then, too.
Main reason why NOrth Korea can't feed itself? The land is all mountainous and not really fit for agriculture... But, no, let's blame communism and not the crazy rulers.
Pol Pot specifically targeted killing whole swaths of the population because in their Marxist ideology, they had to exterminate the educated and land owning elite so that they could start at time zero (literally) to build a Marxist paradise.
But who did the actual exterminating, guy? Pol Pot didn't kill all those folks by his lonesome. Those folks were killed by a population that had been brutalized by a decade of warfare.
Also, interesting thing, that you guys will go on and on about the Cambodian genocide, but never mention the genocide in Nigeria, which killed just as many.
List of wars and anthropogenic disasters by death toll - Wikipedia, the free encyclopedia
The sad commentary is that as human beings, we need very little provocation to kill each other.