Heresy Hypothesis

[Shinylight]

The problem with organised religion is the hierarchy, it no longer becomes about worshipping a deity it becomes about power, a different viewpoint would threaten that power so it is labelled as heresy.

As a religion becomes more dominant in society, as measured by the percentage of the population that identifies as adherents of the faith, it becomes proportionally less tolerant of and more sensitive to heterodoxy and therefore more prone to labeling it as heretical.

So basically you have hit the nail on the head, the more control a religion has the more it wants to keep that control.