I never said "only" I gave an example.
I'm using it in exaggerated terms. Although I agree that being an American includes all demographics, I'm making a point which you just proved. Americans come from all flocks of life. As a person of colour who was born and raised in North America, I can tell you that there are preconceived notions in society. So Clark Kent would grow up in a society where people wouldn't think twice about his upbringing. They'd look at him and go "he's American" and then he would see how blacks, hispanics, asians, arabs and persians are treated and think "damn, that's messed up" while he's actually harboring the fact that he himself is the ultimate immigrant. The audience knows this seminal trait that the other characters in the world of story don't know - this is a literary tool called "dramatic irony" and it's intentionally used.
See above on psyche. Until systemic racism is abolished in North American society, Superman must be white. It's about the dramatic irony and the inner struggles he has to deal with being an immigrant who can camouflage into a society where white men have a very clear advantage.
Yes, I agree that's why they were depicted as white, but for one of the two examples, it really doesn't matter what colour his skin is. It's an arbitrary genetic trait and in the case of Bond it has NO bearing on his character's psyche.
I agree. I'm not suggesting changing his skin colour to be relevant - nobody is. It's actually quite racist to assume as much. You're prejudging a decision based on race. That's the definition of racism. We're suggesting that race should have no impact on the casting decision. If the best actor happens to be not-white, the cast him. If the actor happens to be white, cast him.