crimes against humanity - History

[damn the capitalism]

i've read a lot about communism since years and i beleive in most of its ideas, but the question that i am always asking myself ,is why all the communist dictators were such big butchers !and when we look to khruchev for exemple we call him a revisionist and not a true communist, despite that he didn't kill millions of mpeople like stalin or mao or lenin, ! i think it was their only way to kill to get the power ,but if we used to live in that time ,i think we would live in such a big terror and we would be born afraid and die afraid ,and maybe we wouldn't be that happy with communism because these dictators made a bad image for communism!
so why killing millions ! in terms of this i respect a lot persons (despite their different ideas) like castro or khruchev!