Earlier quoted context omitted.
Those people were not killed by Karl Marx' ideology. It was perverted by dictatorships using it as a banner but it didn't inspire their atrocities. Just like the German Democratic Republic wasn't really democratic at all. Karl Marx' ideology never promoted hate unlike Nazi ideology.
Karl Marx’s ideology promoted the violent seizure of assets from the productive class in a revolution to install communism. The ideology absolutely promoted dictatorship and totalitarianism. There’s no alternative system that can sustain communism, given how opposed it is to basic human nature.
There is a kernel of truth in that communism could not have existed so far, which is why communist states have went for a transitory approach. They could not leap to communism but they tried to work towards it and failed in many places.