@NearDarkroad
@Kireato
They probably aren't stupid, but the fact that they come from the slums and were made into soldiers early on means they know little of how the world works for a free man.
They could most likely do 1+1 and basic math and speaking could be learned if the situation requires it with repetition.
But reading isn't something you learn without trying, or by chance.
They could even have picked up military tactics and other skills as a means of survival in the army or the slums, but that doesn't mean they know anything about how to live as a commoner.
They would have no idea that being able to read is important
as they themselves never actually needed it.
They are for all intents and purposes not much more than slaves, so they would know very little about everyday life outside of combat and the life of a slum rat.
That doesn't make them stupid, it makes them uneducated and uninformed.
And uninformed people make a lot of false assumptions, like believing that anybody could do anything if they were allowed too.