It should be completely up to the filmmaker and the people who pay for the movie imo. They cast Christian Bale as Moses, so it is possible that they wanted to avoid accusations of racism by casting white antagonists as well. Or they thought that the white dudes they cast were better suited for the roles, more famous or easier to get than any suitable non-white actors. I haven't seen the movie, so the comment about racist stereotypes was not in reference to Exodus. The point I was trying to make is that any racist dimension of casting white actors in non-white roles is self-regulated by the market to a large extent. There is no need for social democratic censors to decide production details in movies, such as what race an actor playing a particular role should have (although in my country, Sweden, we have a system just like that).