And I'd be incensed if they took away that aspect of Magneto. I'm Jewish and my grandparents' extended family were wiped out in the holocaust, so I could always empathize with his anger and liked the metaphor of him turning into what he hated the most. See here's the rub; by reaching out to a new audience by changing aspects of a character, you're dismissing your old audience who related to who he or she used to be.
I'd argue that, in the issue of race, white people are not lacking for white characters to identify with, so it does quite a bit less harm.
I'd also argue that it really isn't about identification. It's about representation, which is different. Identification if about getting members of the audience to form an emotional connection with the character on the screen or on the page. A similar ethnic background can be one such way of forging that connection, but there are many other possible avenues, including personal experiences and character traits and environment. I'm not a rich black kid from southern California, but I can still identify with the character of Carlton Banks on the Fresh Prince of Bel Air because I've gone through similar experiences of awkwardness and having my trust in civic institutions shattered.
(As a brief aside, I find the notion that a white person can only identify with Batman because he's white to say more bad things about that person than anything else.)
Representation, on the other hand, is about saying loud and clear that a particular group of people exist and that they matter. We need heroic leads in films who are women and LGBT and people of color, not simply so that those groups can identify with them (although that helps and is a nice thing), but to state very plainly that those people
can be the hero, that they're not defined by nonsense stereotypes and that they're worthy of our respect and of being our surrogates on these fantastical journeys and that they
matter. White people don't need that because we've already been told that, people have been telling that to us our whole lives. We don't need representation because white representation is the default.
I, and hopefully most other white people, will still have the capacity to identify with Superman if they made him black, latino, asian, a pacific islander, native American, what have you. But a group of people, historically marginalized by society, now being represented by America's greatest and most beloved cultural hero? Man, that would be powerful.
And screw the timeline. It's a world where people fly and shoot lasers out of their butt. Why is it so hard to just make it so World War II happened in the 1970's in that world?
Really? Mr T would be an acceptable Harry Potter in your estimation. That's a movie you'd want to see?
No, because Mr. T is an elderly American who can't actually act. Changing a character's race still requires getting good actors who are suited for the part. If they got an 11 year old black kid from London, I wouldn't care. Why should I?
Please explain how it isn't.
On the other end of the spectrum, I would NEVER want to see Daniel Radcliffe play B.A. Baracus in an A-Team reboot. Is it politically correct if Radcliffe complained he couldn't get that role because he's a weedy, white, English kid, and then he was awarded it over other capable actors on the strength of his complaints rather than his talent or how well he fit the role?
That's a pretty glaring false equivalency. White actors aren't hurting for leading roles the same way non-white actors are. And even if Daniel Radcliffe weren't white he'd still be wrong for the part.