You see them switching up race or gender in a movie about people that, to them, are real living people with lawyers?
There was an issue of Flash that actually did that, but as a mocking commentary on Hollywood's history of whitewashing minority characters. They took the Flash's Asian American love interest and made her into a blonde woman.
If it is the new FF cast then it's only a big deal if people make it into one.
Some people should try harder not to be so sensitive. It's not as if marvel sent death notes to the cast and crew of the movie. Its intended to be a joke. It's ok to laugh.