|This is, apparently, offensive to some people.|
As for changing favorites? Yes, they should. They should because otherwise nobody latches on to the characters and they get pushed to the side. By changing Wally West to make him more diverse they take a character and thrust him into the front stage. He now has to be used, he has to be made to work and now we have a major character, a big player, who represents diversity. Otherwise what we have is a bunch of fanboys whining about how their favorite character isn't getting enough panel time because of some "PC bullshit, affirmative action character" who then gets slowly phased out.
This isn't about being PC, it's about inclusion. It's about included everyone and providing a role model for all kinds of people, it's about providing escapism for all people. That's what comics are about, when things are crappy or when you need someone to look up to you have that world and it's important to be able to see yourself in that world. What kind of statement is being made if you have to tell someone that the only way to escape, or the only way you can look up to someone, is if they first imagine themselves as a completely different race or gender? What if when you were growing up the first thing someone said to you was "Alright, first imagine your aren't anything like you are. Step one is you have to picture yourself as a white male because being a black woman isn't good enough. Now have you completely disassociated yourself from everything you are both physically and culturally? Good, because those things mean that you'll never be as good as this white guy. Now that you are distanced from everything you actually are, here enjoy these stories about all the white people better than you." That's kind of a bullshit position and if you hold that position you maybe need to re-evaluate some things.
Finally it seems fans or, at least, a vocal minority of fans, want zero change. They just want everything to be the same always. If that's the case then read the old stories! They aren't gone, they're still there. They'll always be there. They'll never go away. That's the beauty of a print medium. If you're so invested in the status quo just read the old stories. That's basically what you're doing anyway. Why force a brand or creators to write the same shit over and over to appease your fear of change? Just stick with the old stuff you like, shut up and give other people a shot at finding a beloved character.
To me here's the circular argument you get into when it comes to changing race or gender of a character using Wally West as an example:
"Wally can't be black."
"Does race affect the character?"
"No, that's why he should stay white."
"If race doesn't affect the character then it doesn't matter if he's black. Why can't he be black?"
"Wally can't be black!"
And it just goes and goes. Race can't both be something unimportant to a character but also be vital to a character. Either race/gender don't matter and you can make anyone anything or it is the only thing that matters and they have to stay what they are, which is mostly white.
As for the "They don't make Luke Cage/Black Panther white!" argument. Many ethnic characters were created as a commentary on race or specifically for people of other races. They had to be or they would have been pooped out of the white guy machine. So you can't do that to them BECAUSE race would severely affect that character.