When people think of the dark side of religion, the first things that come to mind are usually Islamic terrorists or paedophile priests. Some people regard western “Crusaders” as the big threat. When someone is invoking the name of their god when they’re screwing you over, you’re not going to be too fond of that particular religion.
There is a more subtle problem with religion. It involves what it does for progress. Or more accurately, takes away from progress. Ridiculous doctrines that may have made some sense thousands of years ago are too inflexible to cope with the modern rate of social and technological change. Fundamentalist followers believe in these scriptures completely and won’t hear of any change to the holy word of whoever. Moderate followers may not believe the texts literally but there is a vested interest here too. Any powerful organisation is going to be wary of change since once you’re at the top, the only way is down. So any potential change to the status quo is taken as a threat, rarely as an opportunity. The followers lower down on the hierarchy hear cues that change is bad. And even if they’re not out throwing rocks, too many subconsciously accept the notion.
So there is religious pressure from multiple angles on anyone who wants to introduce progress. Fundamentalists will mindlessly howl about how change is against the will of god or just resort to violence. Religious leaders will only “embrace” change when it is utterly inevitable and until that moment will encourage their followers to resist it. Women’s rights, advances in life sciences and democracy. All good things? All have been resisted on religious grounds at one point or another. For example, the Catholic Church would still rather overpopulation and the spread of HIV than stop discouraging condom use.
How many potential breakthroughs in society and scientific fields have been lost thanks to religious pressures? We’ll never know.