Many ideologies are shaped in reaction to real social ills and real oppression. They are in fact inspired by oppression, they are a plea for justice in an unjust situation. They are most of the times revolutionary ideologies, meant to overthrow and oppressive regime or social system. They are naturally considered liberating forces and attract well-meaning people who support them and leagues of angry supporters. Then a revolution happens, and that ideology becomes the regime or it becomes the dominant ideology. Then, to everyone’s surprise, it’ll turn out to be actually as repressive as the previous system or more, and soon it will lose all the respect it held as a liberating ideology.
But why? Was it because the power corrupted them? Was it because they were never sincere? I think among some individual believers this is possible, but ultimately the problem is somewhere else, somewhere integral to all revolutionary ideologies which makes them potential oppressive opportunities, and what makes them appealing in the first place.