first, to say "they're making spider-man black" seems a bit of an extension. so far as i've seen, they've yet to decide who to cast, and all this is revolving around one comment by some exec.
second, does it really matter? really? how often is a point made about spider-man being distinctly white? is his ethnicity brought up throughout the comic as a point of interest about the character at all? i vaguely remember maybe one self-referential joke he makes about being a white kid from queens. i, as a fan, just don't see it as a defining part of his character; at least insofar as to exclude qualified actors from portraying him.
i understand the argument for wanting to keep the movies reflective of the comics. but this isn't going to be an iron man or an incredible hulk reboot. as far as i know sony still has the rights to spider-man, so they're gonna butcher it just like they and fox have butchered their hero movies in the past. if a better, black actor can give a better performance than a lesser, white actor, i could care less that he's black. it's not such a critical part of the character that it would upset me more than another all-around weak spider-movie.