People trust charismatic people regardless of reason or ideology. It's true that hundreds of people killed their children on the word of Jim Jones, so I suppose you are correct as far as that goes.
If Hitler and Stalin opposed religion it was because it threatened their political power. For nearly fifteen hundred years the kings of Europe embraced religion because it reinforced their power. When the church opposed Henry VIII he killed the chruchmen and started a religion more to his liking. Established religion in the west has always been about power. The "atheist" leaders of the twentieth century came to power in part because they opposed the powerful of the time. The only "ideas" that had any traction during these times were "let's kill the rich ad take their money." Everything else was just marketing.
As opposed to the Modern State which says: "Let's take just a bit from the poor, we can make it up in volume."