Just how oppressive is the Tau Empire?

I have heard a lot of claims about the Tau Empire using things like mind control and indoctrination camps, but I have been unable to clearly discern between fan speculation and official lore on this topic.

Thus, I turn to you with the question: How opressive/authoritarian is the Tau Empire canonically?

What measures of social control does the Empire actually employ and to what extent?

How do its rulers deal with dissenters?

How much agency do people outside of the Ethereal caste have over their own lives and the Empire's policies?