I never look at changing the cast as "insulting" the real world just doesn't look like the cast of these books especially big city population centers people casting don't really have a choice the cast will stick out either way. I don't think that they think something would be loss if the main character was changed, it is just the easiest route to avoid fan backlash while making a modern change is leaving the main character as is in the books while changing the cast. In reading through this topic I honestly don't think changing Superman race would have the biggest impact possible the people who are against would just be able to go that is not my Superman. In hearing people talking the biggest impact would probably be changing Lois Lane to a Black character then some Superman fans having to deal with a character they see themselves in navigate through sticky issue of race. Just imagine a comic cover/movie poster of a White Superman and Black Lois Lane kissing it is something that shouldn't cause a big deal today but we all know it would cause a meltdown on interwebs. It is probably more impactful to have character in his iconic form deal with issues of race from a personal level in this case.
Didn't Superman concept start off as evil scientist ? He may have become rebuke I don't think he was designed to be that initially.