Please inform yourself about communism and go read a history book before making these claims. The regimes that killed these millions of people, and I'm assuming you're talking about Stalin, Mao, Pol Pot, the Kim Dynasty etc. here, are not, in fact, communist. Yes, they write that on their banners, but the Nazis also wrote socialism on their banners and they were not socialists by ideology. Neither is North Korea democratic, even though they have that in their official name.
Communism is, in a nutshell, an ideology that puts the community (hence the name) in the center and considers all members as equals. There are no stakeholders with more power which comes from owning land, for example, as all means of production, as Marx called it, belong to the community itself, and therefore to everyone who is a part of it.
Stalin and friends used communism as an excuse for a power grab, not too different from how Hitler used socialist rhetoric to sweet-talk the worker demographic, or, to use a more recent example, how ISIS tries to justify terrorism with religion.
I'm not judging here. You're free to believe that communism is stupid and bad and completely removed from reality, but saying that it was the ideology which killed those people is simply wrong and a piece of misinformation as far as history goes.