Cuz their pedophiles
All Religion started as great, their teachings are great too but the problem starts with the modernization. Religious people wants to remain in their original state as close to nature and God but with modernization and broad thinking or develop thinking questions everything. Like example - in a religious book it's written don't eat anything from areas across the river stream otherwise you be punished. Somehow it was right at that time because their might be a plague their but with time plague ended and society thrives there. A religious person will never cross the river but a normal person will. Religious person seeing this act as an act against God words and might kill the person in the process and call it god punishment.
If religious values updated with time then it won't be a problem but with churches they still believe themselves superior as they colonized most of the population and basically try to impose themselves on other. That holier and superiority and control over other belief makes them villian.
The catholic church had so much corruption ... it ransacked so many nations and was used as a political tool to destroy pagan societies and was deemed the "Truth" The blind following and fanaticism had so much power. It lays bare to hypocrisy, corruption and mental gymnastics. Basically its easy to make an annoying character out of it and a good plot device.
And also you already said it, it justified slavery... that itself is one of the most horrifying things ever. And did you know the british empire had a different bible for the slave it omits the book preaching about freedom. Thats real life , and its not hard to imagine how they can be evil.
religions Abrahamic and non Abrahamic ones can be turned into vessels of opression. i mean one of the biggest perpretators obviously is christianity with slavery and colonisation. but also in my cultures religion, we have stuff like caste that has been used to supress and divde people. a lot of religions have a concept of preserving their ideas, but human nature for the most part is always changing. what works now may not work in the future, and the same problem sometimes needs different solutions.
like someone pointed some off the teaching worked at the time for whatever the problem was at the time. but things change, not only through modernisation but within a 100 years the cultures change drastically, and a friction between religion and present day can cause a lot of harm. so because of that religion ends up being something that has caused harm and something people to this day have a lot of critism or resentment towards.
i think the reason christianty especially has a lot of stories where they are the antognist is because theyre one of the biggest religions, their history of colonisalism and christian emphasis on converting people. christianty alone isnt the only relgion with its faults or history of violence and opression obviously but in recent history is has done a lot of damage.
Anyone know the reason why religion or church is always an antagonist in stories from manhwas and mangas? Like theyre always the bad guys who try to do everything for justice from their belief of God? Im catholic but Idk the history of what christianity has done to the world or the impact of it. One thing I know is that christianity was used as a reason for slavery to be legalized.