Rome's culture and traditional was fundamentally broken; it no longer served the needs of the Roman people, and if Christianity hadn't popped up, it would have been some other system of reform instead. The status quo was unstable, rapidly deteriorating. You may idealize the religious tolerance of their polytheism, but what that matter if it isn't actually serving the spiritual needs of the people?
Rome in the end was a decadent, but brutal empire full of slaves. And to a slave christian salvation sounds great.
But before there was a empire with emperors taking up the idea of becoming gods themself, there was a republic. And also after it became an empire, they did not have a institution like the inquisition shaping thought and banning heresy baked into their system.
This is the fundamental difference that I see.
In medieval times being expelled from the church was pretty much a death sentence. In roman and greek times for most of its existence not really.
I’m not sure there necessarily was that much progress before that, though? With some exceptions ancient societies were highly stagnant especially technologically in contrast to high-late medieval Europe.
Also plague, climate change and demographic collapse kind of directly kickstarted the dark ages.
And in ancient greece there were already concepts of a steam engine. I call that signs of progress not happening for a long time after that.
I see you're one of today's lucky 10,000! https://en.wikipedia.org/wiki/Diocletianic_Persecution#Great...
"So also in non christian societies people were killed for having the wrong ideas, but comparing greece or early rome with the christian empires"
Why do you think you told me something new?
This is a modern view with hindsight bias. In the ancient world, the existence of many gods did not imply peaceful co-existance, but very heated rivalry and politics.
Ironically pagan authors of late antiquity were the "conservatives" in our modern sense. Pagan literally means "farmer" - it might have similar implications to how we would call someone a "redneck" today. At the time, they were opposed to foreign gods and new influences on their traditional and respectable Pantheon.