It’s particularly ironic to me, when you look at modern Catholicism. The church that once persecuted Copernicus and Galileo now advocate for science and embrace the evidence supporting evolution, albeit from a creationist angle, and, as an institution, do not teach a literal interpretation of the Bible. Which isn’t to say they aren’t still backwards AF. 

BTW - I suspect that if folks respond to this, there will be assumptions about what I believe. I am not an atheist. I do not believe that Christianity, or Islam, Judaism, Hinduism, Buddhism, or any organized religion is “right.” I guess I’d fall under the “more things in heaven and earth” camp, though I’ve always been particularly intrigued by Buddhism. But it’s also pretty easy for me to argue things from a “Christian” perspective, since I grew up in a Christian household, and it just feels to me that trying to dismantle that religion using assumptions about God and the Bible misses the mark, considering that the earliest stories within were first told sometime around half of 1% of humankind’s existence on this planet ago. Same for all the other faiths. 

Religion is just how we express belief in something truly beyond our ability to comprehend, by choosing to place that belief into something we rationally know cannot be true. The problem, as always, is when people are so insecure in their beliefs that they externalize their doubt, villainize those who believe differently, and convince themselves that their doubts will magically go away if only they “convince,” often by force, the “heretics” and “skeptics.” But obviously that’s just my opinion.

I've long believed it was a product of evolution - we as a species have evolved under the evidence that there's safety in numbers, and so we tend to congregate and look toward one leader to tell us what to do. We also are hardwired to mistrust "the Other," which can be anything from someone who just looks "weird," or has a different skin colour, or comes from a different country, or even just a different part of our home city, or, yes, has a different religion from us. 

But we as a species are also only really capable of having actual relationships with, what, 100, 200 people at the most? Our evolution hasn't kept up with the speed of human advancement, where a person can now be adored by millions, or even billions in some cases. I think that's partly why people who become impossibly famous tend to go a little haywire and do destructive things, and in cases of so-called "ultimate" or uncontested power, we end up with death squads and mass graves, especially when faced with that dreaded threat of "the other." 

I feel like anyone who claims that behaviour would change if religion was gone is deliberately ignoring natural human behaviour, not to mention human history. We'd still do it all, just for different reasons. That's the real problem we face, and there's no simple solution to that one.