Organized Religion
While religions have historically maintained strict hierarchies and doctrines, the human tendency towards corruption tends to subvert these organizations towards evil, as it does with any large organization. While the Catholic Church is probably the best-known example of this thanks to the Protestant split and well-publicized scandals, this problem is rooted in human nature, so it affects all religions and denominations.
Yes, it is certainly true that there will also be good people in these organizations, but the power offered by organized religion will always attract the wicked and deluded. Whatever their petty desire is, be it control over the lives of others, a shield to protect their sins from mortal eyes, or to unleash their inner demons on the world, they see religion as a tool for mortal benefit, not divine enlightenment. They may make the conscious decision to infiltrate the religion through deception, or they may mistake their misguided delusions of grandeur for righteous zeal, but they will always find their way in because the good people in the organization are only human and will make mistakes.
Organized religion also makes it difficult to identify and deal with these evildoers since their status within the hierarchy gives them presumptive protection from scrutiny. Organizations also typically resist the removal of bad actors within their ranks since it is easy to stretch forgiveness too far and organizations often view the removal of highly visible members as a public embarrassment.
However, since people do need religious instruction to avoid falling into sin, some form of hierarchy is needed. The first step towards God must start in the home with parents teaching their children the basics, and theological discussions between peers are a vital way to challenge ideas and explore alternative interpretations in search of the Divine Truth. Wise men, both living and dead, also have a role to play in elevating the public discourse, but their public notoriety makes them susceptible to the dangers of organized religion, so it is essential to listen to many different wise men and give careful thought to the merit of their words before giving them credence and reward.
Thus, any organized religion, no matter how pious it begins, is prone to infiltration and subversion by evil forces, and the only antidote is a flexible community of the righteous able to learn from each other and identify the inevitable bad actors within any human society.