This not a mainstream view today. Archaeological and anthropological research has overwhelmingly indicated that pre agricultural societies were incredibly violent, moreso than agricultural ones. Pre agricultural societies averaged between 15 and 40% of people dying violent deaths (as in, died at the hands of other humans) as compared to 3-5% in agricultural societies. It drops even further for industrial societies. To put this in perspective, about 1.7 to 1.9% of people died violently in the 20th century.

The view that pre agricultural societies were peaceful was not based in evidence, but based in wishful thinking: if civilization corrupted people then we could fix it by undoing this corruption. This was a popular belief around the 1960s and 1970s when there was little to no hard evidence on the behavior of early human societies.