well, it gets into the idea that a bad species has to have some sort of toltarian regime, and with that a type of Stasi/gestapo/kgb system that Watch's the population, and to protect the system. We have that with the Romulans, Cardasians, and probably other species. and in latter shows, shown that there is some type of resistance movement, or that the people are repressed by there overreaching government. That the people are generally good, but there government sucks. If you take a look at our world history, you'll see that most of our history is a history of oppression. How many pharaoh's, Kings, Queens, Dukes, Emporors, etc. Only recently, With the US being one of the first, is democracy. Regular people leading, not royalty, or some other type of family rule. ( though it doesn't seem like it sometimes, with family's like Kennedy keep on getting elected forever as an example). And who's to say the world wouldn't go back to an opressive system in the future? Look at the Terran Empire. For the Romulans, this may be a "phase" in there history, maybe in the past they were a more democratic, open society, then something happened, maybe a plague, maybe famine, and the government took more control of the system for the duration, and as always happens, once a person/people get power, they are reluctant to give up that power. They may have taken control of the system during the emergency, and didn't give up control afterwards, and using past examples in our history, with the Gestapo, Stasi, created the Tal Shiar as a means to "Protect" the system. Listening in on the populace, making agitators "Disappear" Etc. After hundreds, maybe thousands of years, systems rose and fell, and this is only the current iteration of there system and given the natural progression of time.. that was interrupted by the Supernova, they might have gone to another system. Maybe like England where there monarchy was relegated to more "Honorary" position, and the senate would be like the House of Lords, and maybe the creation of a House of commons. So just saying, it doesn't have to a Mono Culture that has existed In the same way since there landing on Romulas.
Please, now you are potentially summoning anger of history buffs who might tell you that different concentration of power isn´t necessarily "opression" and that concept of democracy and parlamentarianism kinda predates modern history, but even I would prefer this wouldn´t turn into angry discussion about terminology. Obviously, if you are talking about unviversal rights, thats something different...
I'm not a big history buff, so sorry if some terminology isn't correct or over simplified... or flat out wrong.. Just trying to say that most of the history of nations/government/rulers have been power concentrated in a few, and the regular people haveing almost no say in it. You live under a duke, what the duke says is law, the blacksmith has no say in it. And usually nobles fighting among each other and them not caring on how many "Peasants" died. Life was cheap back then.
Thus adding credence to my theory that Vulcans are the true source of every problem in the ST universe.
He seems to allow for discrepancy. Believers in ancient pantheism, modern imperial worship, and doubters of both. Maybe it’s the same for this monoculture. The Star Empire is vast and some follow these ways, others the honesty of the QM and others a range in between that are closer to the canon/lit.
And there is more. Specific to Nerak and to Romulan gaming preferences... https://michaelchabon.medium.com/two-final-notes-on-romulans-8d05e27ee9fa