Virtually, every single communist country has killed it's own citizens and committed human rights violations in the name of government will.
In fact, the worst mass murders in the whole history of human beings were committed by country's with communist regimes. Millions of people died under the communist regime of USSR, Red China, Cambodia, and North Korea.
I think the real question is how many more people would have died under Argentina's communist regime as opposed to those who died under Pinochet's?
That's totally true. As have a great many non-Communist countries. Communism is an enemy, but it's not the only enemy. We should oppose totalitarianism of all stripes, whether it's militarist, Islamist, fascist, Communist or anything else. Allende and Pinochet were both bad.