The problem with that idea is that it's flatly contradicted by "Face of the Enemy" and, later, numerous DS9 episodes, which firmly establish that the Romulan people live of terror of the Tal Shiar -- they have plenty of horror stories about people being dragged out of their homes in the middle off the night and then being "disappeared" by the Tal Shiar.
I don't know that Romulans live in terror
of the Tal Shiar - maybe they consider it a necessary adjunct to a powerful government that can protect all Romulans. A few traitors being "disappeared" may be considered acceptable losses. They're not humans and we don't have any real understanding of their mindset, other than that we can assume they won't react like humans do to everything.
We really don't know much about individual Romulans or how they live at all. That's part of the problem - we need to know more. But when they're drawn out in more detail, I certainly hope they are distinct from human attitudes and preconceptions in many key areas, and one of those areas could be that while humans would react badly to having their own Tal Shiar running things, the same isn't necessarily true of Romulans. And their definition of an acceptable democracy isn't going to be the same as humans'.
You know, I've been contemplating how the Romulans might characterize or justify their form of government and the term "post-democracy" keeps popping in my head. I'm not entirely sure what I mean, but I think the Romulans might have reached a mindset where they still see the need for individual freedoms, but "understand" that sometimes for the greater good of their people their individual freedoms must give way for the good of the state, hence the justification for the Tal Shiar and the heavy military influence
Yeah that's my suspicion too. But they didn't necessarily "evolve" to that point. That just may be natural for them, based on their culture and the way they think. It would synch up well with the question of "what do they use to create a functional society if they don't use logic?" Instead, they have xenophobia, aggression turned outwards. But that implies that, turned inwards, the inverse happens - the community eclipses individuality, so that Romulans have no expectation of individual rights the way humans do. And that's not because they're oppressed - it's because that's the way they are.