Yeah, even for Cassius, I don't get his angle here.
He doesn't understand that propaganda != history. Ask any FOX news viewer and they will say the same thing that Cassius does. "So what if its propaganda. Its history/news."
Virtually all forms of education can be interpreted as propaganda in one form or another. This is not a bad thing, since the world would be a pretty chaotic place if we simply let everybody figure life, the universe and everything for themselves using their own peculiar form of reasoning. Indeed, when it comes to the type of education (low-level, examination orientated) that we're dealing with, individual thought should be actively discouraged (indeed, I vaguely recall one of my History teachers telling me that; I think she said that I was 'overthinking things' by saying that the religious policy of Mary I could be thought of as equally significant to that of Elizabeth I
).
Basically, the teaching of History is always going to be biased in one way or another (I remember having to study the history of Britain's involvement with slavery in Year 9, which basically almost consisted of long, loooong descriptions of the conditions aboard slave-ships, and a very brief mention of Wilberforce!). So, to my way of thinking, the job of those that set the curriculum is to ensure that the curriculum is biased the right way, not the wrong way.