1) Michael B. Jordan was cast because he previously worked with Josh Trank. Josh Trank directed Chronicle, another science fiction film produced by 20th Century Fox. Trank is also the director of The Fantastic Four and he brought Jordan along with him. The situation between Trank and Jordan is no different than Johnny Depp and Tim Burton or Quentin Tarantino and Uma Thurman. Directors enjoy working with the same actors, if possible.
Although liberals may have celebrated the casting as a diversity call, the reality is that Jordan's casting was good old fashioned Hollywood cronyism and nothing more. Here is a quote from Miles Teller on how Trank handled casting (Teller plays Mr. Fantastic in the upcoming film).
"I know Josh really had to [pull for me]. Josh did for all of the characters. For Jamie, he really vouched for [him]. For Mike, he was like, ‘This is my guy’ from the bat."
http://www.themarysue.com/miles-teller-fantastic-4-casting/
Political correctness had no part in the casting of Michael B. Jordan as the Human Torch.
2) Lucius Fox's ethnicity is a non-factor of his portrayal. Fox could be any ethnicity and his role in the Batman mythos would remain unchanged.
3) The ethnicity of non-White characters is changed all the time in comicbook films specifically, and movies in general.
- R'as Al Ghul: A 500 year old Arab, whose name is itself in Arabic. In the Nolan Batman trilogy, R'as is played by an Irish White male. No one complained.
- Bane: In comics, half White, half Latino (the fictional country of Santa Prisca). In the Nolan trilogy, Bane spoke no Spanish, had an accent that had little to do with a Caribbean region Spanish and was played by fully White Tom Hardy. No one complained.
- Chapel: In the Spawn comicbooks, Chapel is a Black male. In the movie, Chapel is turned into a White woman named Jessica Priest.
- Terry: Al Simmon's best friend, also made into a White person, though originally Black in the comics. The producers publicly stated that they changed the characters into White people because they didn't want to stigmatize the film as being a "Black people movie." And even with that on record, no one complained.
- Talia Al' Ghul: Arab daughter of an Arab man. Played by a White French woman.
- Avatar the Last Airbender: Aang and Katara, played by White children rather than by a Chinese and Inuit child respectively. That time though, people did complain, quite a bit.
I could keep going on, but the point is made. It isn't as if "race bending" (the pop-culture term for changing the ethnicity of an established character) is a one sided affair. It happens more or less across the board, though the impact/consequence is not equivalent for all ethnic groups.
4) The primary argument is not about whether or not established characters should be subject to race bending or gender bending, but rather the issue is whether or not such actions are detrimental to a particular ethnic community or the accuracy of the character's established narrative.
If race bending alters the core mythos of a character, then it should be avoided. For instance, Magneto's entire world view is shaped by his experience as a Jewish child in a Nazi concentration camp. Having Magneto not be Jewish would undermine the core mythos of the character.
Race bending Lucius Fox would be unimportant as his role and motivations are not attached to his ethnic identity. Conversely, changing T'Challa into a White person would be damaging, as it would white wash a narrative about Black Africa and erase a visible minority.
Likewise, making Wonder Woman Mexican, Black or Chinese instead of Greek would pose a problem similar to making T'Challa White. Why? Because Wonder Woman being Greek is a significant aspect of her overall characterization.
The situation is not simplistic, and each alteration requires an examination of the specific context brought about by the change. There is no hard and fast rule of "every character should stay the same" or "change every character for diversity sake." Sadly, the discourse on diversity in comics is rife with the voices of the prejudice, bigots, the ignorant and the entitled. You have very conservative bigots and extremely liberal zealots that make the entire situation untenable, and both factions pose the same danger.
In the end, these are narratives about fictional characters: they do not exist. Therefore, there is no obligation to keep their characterization set in stone. They will change with the times, and the times will also change. What is meaningful now may not be meaningful later. Getting hostile or irritated over movie casting choices...well...life is truly too short for such a waste of a resource as precious and limited as time.
