Daniel,

1. Myles Morales is not African American.  He is Hispanic/Afro-Caribbean.
2. Ultimate Nick Fury did not “become black out of nowhere”.  He was always black.  Did Ultimate Wasp become Asian “out of nowhere”?
3. Victor Alvarez, Ava Ayala, Blade and Kaluu are members of The Mighty Avengers, and neither of them are African American (Blade is British).
4. If white readers supported existing African American/Black characters, there would be no motivation to “force” anything.  Yet, you can’t find a single black character in Marvel that can sustain an ongoing title no matter the quality of the character or the writing.  Mighty Avengers selling low is a good example of this.  Clearly you yourself are not buying it.
5. People who make these complaints seek to maintain the status quo.  If books starring black or non-white characters don’t sell, then tough.  Be happy with the crumbs tossed by including them as the one or two minority members of the white led and dominated team.