I wasn't under the impression comic fans represent most people.
White man/black woman relationships have been on television and film for decades, including on one of the most popular shows on television right now. I think the issue here is more about source material fans throwing fits over "drastic" adaption changes. The last recent example I can think of was with Game Of Thrones last year, when Pedro Pascal was cast as Oberyn Martell; fanboys screamed he was "too white" and it caused a stir.
And then there's the little chick in Hunger Games who people were upset is black; yet no one complains about Jennifer Lawrence being too white.
TLDR: Nerds gonna be nerds. Johnny Storm is white, sure...but being white doesn't really matter to his "character." It's not like say...making the Black Panther white.
You have more faith in Fox (and your fellow man) than I do, I guess.
Well then, I'm all ears: why do you think we have racially mismatched siblings in this movie? What do you think is the reason Sue isn't being played by a black actress?
I haven't read anything, but I'm going to assume Johnny is her adopted brother, which is an interesting way to be diverse without being
too diverse. I remember a GAF thread about the casting call not having race restrictions, and people were suggesting Jordan as well as Donald Glover.
A better question, to me, is: if someone like Zoe Saldana had auditioned for the role, would Fox have rejected her on the basis of race? Honestly I doubt that, especially for Zoe, given her previous work with Fox and the fact that she's somewhat of a reliable face for these types of films. Whereas Kate Mara isn't necessarily some big box office name/draw.
Honestly, the only notable actor in the main cast is Jordan. I think the film is going to bomb because it doesn't have a reliable attractive white male lead. Mr. Fantastic isn't really a "hot" character, but given Marvel's previous success at casting male leads I still find the choice puzzling - the actor doesn't have a chin for christs sake. Same with Grimm; he'll likely be CGI for much of the film, but you would think Marvel would cast a heartthrob to put women in the seats.
