Who needs theory? Practicality tells all.
Extreme ideologies don't value free speech, because free speech allows the unwashed masses to communicate to each other just how ridiculous they think your ideology is. This is true regardless of where an ideology falls on the oversimplistic "right-left" spectrum: North Korea, Fascist Italy, Communist Russia, Oligarchical-Capitalist Russia, Cambodia, North Vietnam, Burma, Communist China, pretty much the entire Middle East, etc. The list goes on and on and on.
Suppress free speech and criminalize dissident thoughts, and you establish a social basis for staying in power - for the good of the people, of course.
It's unsurprising that extreme ideological adherents are always united in at least one common idea, regardless of the actual content of the ideology they are espousing: the belief that people themselves don't know what is best for their own interests and must be closely watched and shepherded (and culled) if they fall into an annoying habit of thinking on their own.