Social communities evolved into existence and they require an anti-anything goes set of rules to be sustainable. That happened without a god well before there was a god. Heck communal animals exhibit this level of restraint.
I think Rome is an interesting example - with orgies and according to Alan Watts slave girls were fed to lions to entertain the crowds...
[YOUTUBE]https://youtu.be/qOZqGUCrje8[/YOUTUBE]
Sometimes the emperor declares himself to be a god....
This is a myth about ancient Rome. The reason Christianity has the moral values it does is because it's a product of the Roman empire. Christian morals are Roman morals. The Bible is basically Judaism shoehorned into a Stoic box.
Both Epicureanism and Stoicism teach the same thing as would later pop up in Christianity. Don't give into carnal pleasures. Be disciplined. Don't be overly emotional. Be frugal. Don't waste money. Honour your family. Be dutiful, etc etc. These two philosophical/religious school were totally dominant in the period when Christianity was formed.
The reason why we know so much about Roman decadence is because the Romans themselves were horrified about decadent Romans, and wrote about it. These authors were then copied and kept alive by Christian monks. As a way to prove how Rome had been decadent and fallen and now with Christianity it was now a moral place. In spite of nothing much changing. It was the same place before and after the conversion to Christianity.
Juvenal was a pagan Roman author and playwrite writing satires where he mercilessly mocks decadent Romans. He comes across as any later Christian. His moral values are indistinguishable.
https://en.wikipedia.org/wiki/Juvenal
The main difference between Christian and pre-Christian Rome was one of free speech. But it wasn't Christianity that created this culture. It was Augustus, who destroyed free speech in order to destroy the Roman republic and make himself dictator.
When Nero singled out Christians as horrendous and an evil conspiracy and persecuted them. Nobody bought into his bullshit. For this mobs stormed his palace and forced him out of power. These weren't Christians. These were pagans. Everybody thought the way he treated Christians was immoral. And above all, everybody thought the way Nero was behaving, ie a life of orgies and sex, was immoral.
I suggest reading about the pre-Christian pagan cult of Isis. It's basically Christianity. It's exactly the same ideas and faith. Just with other symbols. Born in Egypt around 300 BC and spread throughout the Roman empire. Roman's were really into Christian style moral values long before Jesus was ever born. It goes all the way back to the foundation of the Roman Republic (510 BC) and probably even further back.
https://en.wikipedia.org/wiki/Mysteries_of_Isis
The Roman gladiatorial games have at this point become largely mythic activities. Gladiators were basically WWF style wrestlers. It was all staged for entertainment and gladiators rarely died. Baked into the numbers of those dead in the gladiatorial games were condemned prisoners. Those sentenced to death got executed in the arena. No, they didn't get to fight as gladiators. They were just killed. Just like Europe continued to do after Rome became Christian. The Roman gladiatorial games was mostly just stage shows to celebrate various significant events. Comparable to us today going to the movies.
Christians criticizing the immorality and decadence of Rome is stupid. Because they are basically criticizing themselves.