I think Fremens were every bit as brutal and barbaric as Mongolians during those ancient times. They killed billions of people across the known universe. Let me bring in the lines from 'Dune Messiah', "Stilgar," Paul said,"you urgently need a sense of balance which can come only from an understanding of long-term effects. What little information we have about the old times, the pittance of data which the Butlerians left us, Korba has brought it for you. Start with Genghis Khan." "Genghis ...Khan? Was he of the Sardaukar, m'Lord?" "Oh, long before that. He killed ...perhaps four million." "He must've had a formidable weaponry to kill that many, Sire. Lasbeams, perhaps, or..." "He didn't kill them himself, Stil. He killed the way I kill, by sending out his legions...