Reimian Empire

even a particularly sharp manifestation of elitism (we have incorporated you, but we will not consider you citizens, sorry, you haven't earned it)

Ment, are you sure you read their description?

they are not distinguished by their intelligence. Because of this, they were never recognized as citizens of the empire, and, as a result, they are, with rare exceptions, forbidden from leaving the borders of their native swamps.

Added 13 minutes later

Well, what else can you do with hopelessly stupid creatures?

The fact that some can earn citizenship and are trainable already suggests that they are not hopelessly stupid. And in general, someone who doesn't have animal intelligence can be quite well socialized. For example, in the Israeli army, there is even work for people with intellectual disabilities.
In general, it's strange to hear this from someone who expressed a desire to become as stupid as possible. And who believes that stupidity is a positive trait.