About the most important tenet of communism is collectivism. When you attempt collectivization on a national level, there's always a significant portion of the population who doesn't want to play along and wants to keep doing their own thing. That's the end of the road for your political system unless you do a bit of mass murder, which is why every "successful" communist state resorted to that.

So yes, of course, no political ideology has "let's murder millions of people" as its founding principle. But some political systems require it.