Again, you've got to be careful here, because historical and dialectical materialism makes this tricky. The pure idealist position -- not saying you're advocating it, but it's certainly easy to fall into -- is that of Rosseau and his ilk: under primitive communism, humanity lived an idyllic life, and then property and the agricultural revolution entered and started us off on a long train of opression and conflict within the species. There is truth to this, but isn't the whole story. As every new mode of production brings with it an increase in human power over nature, it also brings an expansion in concrete "rights," because humanity can now better defend itself against external nature. Thus the great slave civilizations of the ancient world were actually an improvement on hunter-gatherer society, and feudalism was an advance over slavery, since the average medieval peasant lived a better life than the average Roman slave, and the average Roman slave was better off than the average tribesman under primitive communism (if only in terms of life expectancy and being able to preserve his subjectivity in the face of hostile nature). The long view is that humanity moves from primitive communism to advanced, technological communism, with everything in between a neccesary transitional stage as humanity pauses and asserts its control over the external world. But what we need to be careful of is applying a moral valuation to any point in the transition. The level of social development can never be higher than the level of economic development, and at any point in history, humanity basically tends to the most equitable arrangement possible under the current development of productive forces.