Early on, Christianity was the new atheist movement. They rejected the roman gods, and were called atheists by their opponents.
I think its a law of human behavior that groups divide, and the more encompassing the group is, the more people are pulled to divide. They'll find some little thing which seems inconsequential to an outsider and they'll form teams, and the teams devise purity tests to attract the "true believers" (in any domain - only coincidence that the term is bring used in this context), and people who rightly object to the shifting goal posts of the purity test are ostracized, and they eventually have to make a choice : give up and conform, or don't.
Before the Protestants left, the Catholics left EO. Within catholicism there were bloody splits before the Protestants won - the Cathars and the Waldensians, the Arians, the Hussite's, etc. Within EO there were bloody splits. Augustine basically lobbied to have heretics murdered by the state. Justinian rounded up and murdered his Italian rivals on the religious grounds of them following the teaching of Origen.
The Protestants are remarkable only because they won. It took 1200 years for any heresy to win after the consolidation under Constantine. Before that, they were routinely murdered en masse.
I actually disagree with a lot of Protestantism. Calvinism is pure barf. The motivation for Anglicanism is silly. Luther himself didn't even want the revolution and spent most of his life trying to stop it. But... I like the fact that they did it. Not the war, and not the specific beliefs, and not the loss of tradition, and not the way modern Protestants mostly have no idea what their denomination even means... But the fact that they left and got away with it - that bears God's fingerprint, IMO.
My comment above was a continuation on my thoughts on idolatry, combined with some revelations from reading Zhuangzi, an ancient Chinese philosophy book, which is one of the foundational books of Daoism. It made a really solid point that trying to improve things has only ever harmed them. I can't do it justice, but its worth reading just for that line of reasoning. So I was thinking... Did Jesus ever actually say anything like, "be nice?" There's "do into others" - but if I'd prefer truth over niceness, then my directive is to say the truth, not the nicety. And Jesus **_did say_** to pursue the truth and the truth will set you free.
So I'm thinking modern Christianity has made a terrible sacrifice. It sacrificed Truth for Charity. And anything not-truth is idol, because idols are false images. All things are images, but not all images are false.
Still, I'm hoping someone will try to make a real case that Christians have to be nice.