On questions like vengeance opinion is divided. What appalls us then about atrocities is the degree to which they seem unnecessary and deliberate bloodshed. The Nazis hare-brained racial mysticism and the Communists brave new world of man remodeled to the socialist ideal strike most of us as horribly inadequate reason for so many deaths. To their adherents however, these ideologies justify everything by the promise of utopia. Here we see the twofold influence of Christianity, our great inheritance from Rome.
Communism is after all, a corruption of the Christian moral order, wedding it to compulsion.
Both were preaching an alternative religion, developed like most religions out of the ones that came before. When we weigh Rome on the scale of necessity they are found wanting, though some mitigation can be made for the limitations under which Roman justice and Roman administration labored. The best we can say of the Romans in the end is that they felt their own moral inadequacy, they embraced a better system - Christianity. Rome's greatness is in the individual not in the conglomerate.