Absence of evidence is not evidence of absence; this is even more true when appealing to prehistoric times when indeed we have very little evidence for much of anything. What we do know is that in the eras since things have become somewhat more clearly recorded that slavery, war, rape, etc have been ubiquitous. Even Native Americans, sometimes pictured as peace pipe smoking peoples in tune with and peacefully coexisting with nature, were engaged in warfare, slavery, and so on long before Europeans arrived. And as people sometimes confuse these sort of statements - that is in no way mitigating what happened to them. But rather just an accurate reflection of history.

We can also see glimpses of prehistoric societies from looking at people who stayed isolated from modern society. The Sentinelese people are a group example as they are one of the only remaining uncontacted peoples. [1] They are a violent warfaring people whom have murdered numerous people who have gotten too close to them. And there's nothing to blame here except their, and 'our', own nature. And one annoying aspect of society is that we must adapt to the lowest common denominator in matters such as this. Groups that are unskilled in warfare are rapidly 'replaced' (to use quite the euphemism) by those that are!

And as somebody else mentioned you can even see similar behavior in other non-human primates species from which we share a common ancestor, such as chimps. They, to this day, gather into bands in large part to go kill other bands and expand their territory. They also have a habit of engaging in some rather sadistic behavior to the losers. The only reason this warfare is not expanded to tremendous numbers is but for a lack of higher intelligence required to develop the tools and structure necessary for such. And as group sizes increase, so does the probability of splintering of a group.

So to appeal to the noble savage requires that we go war driven -> tranquil -> war driven. And that tranquil period is, conveniently, only when we have insufficient evidence to say anything one way or the other. This is not logical.

[1] - https://en.wikipedia.org/wiki/Sentinelese

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One final point should also be made since it's not commonly considered. Today live in what is almost certainly the safest period of human history - ever. Something few realize. Today there is less than 1 death per 100,000 caused by war - worldwide. The world population of 'humans' varies radically by era. But in the era's we're referencing, you'd be looking at a max population of some single digit millions. If they were comparably safe to today, you'd see some 10 or 20 people dying as a result of warfare per year - in total. I don't think it'd be be controversial to suggest that number was likely markedly higher.