In defense of people who believed this, they were thousands of years away from anything being better on earth.
Like imagine living through the decline of a brutal slave empire, which took centuries to fully collapse, and the thing that replaced it was fucking internecine Feudal warfare for another millennia.
Unironically, whether you can stomach all the atrocities that happened afterwards or not, until the rise of Islam and its golden age, you would be pretty justified in thinking the world was never going to be better than it was in an age when most people were still utterly miserable.
That mindset about “everyone deep down wanting what they think is best for the world” is a baby brained attitude you must grow out of.
At the very least, because it isn’t true. But more importantly, because it doesn’t matter.
I imagine lib girl doesn’t feel this way about the unarmed people the cops shoot in the street. Were they all bad people on the inside?
There’s no way to convince someone out of this, it’s literally a form of immaturity. They have to see evil directly in front of them to truly understand.