Answer: Both sides confidently believe that if all the other guys not already with them would just get the hell out of the way, spectacular human progress could be made. Here’s how John Gray puts it in his excellent book, Black Mass (2007, 25-26):
Modern political religion may reject Christianity, but they cannot do without demonology. The Jacobins, the Bolsheviks and the Nazis all believed that vast conspiracies were mounted against them, as do radical Islamists today. It is never the flaws of human nature that stand in the way of Utopia. It is the working of evil forces. Ultimately these dark forces will fail, but only after they have tried to block human advance by every kind of nefarious device. This is the classic millinarian syndrome, and in the forms in which they have shaped modern politics the millinarian and the utopian mentality are one and the same.
Prometheus Unbound 