This is bullshit. IT's practically Marvel saying "if you don't like our comics you're racist/sexist". Fuck them.
Marvel comics sales has gone down because because the quality of their writers has hit rock bottom and they still rely on that hack Bendis for too much.
For too long the comics have just been used to make crowd-pleasing headlines and events to bolster movie sales - There's been little attempt at telling good stories in the comics themselves for a long time.
People LIKE DIVERSITY. Honestly, some of the most popular characters have been minorities - just look at the popularity of Cage, Panther and Storm. The readers are very accepting of any characters, even those taking over the mantle of other heroes.. IF THEYRE DONE WELL.
I actually like the new Thor, it's written well and works with the previous continuity to advance new characters. Agent Venom added a hero with a disability and simultaneously grew the characters of both and Flash and the Symbiote and told good stories. This is what we need more of.
Riri... She was making headlines as the next Iron man before anyone really a clue who the fuck she was. Iceman was SWAPPED to being gay against decades of being straight for his new series (we saw every thought in his head in "thought bubbles" and he was living with all the worlds greatest telepaths - like it or not, it IS a retcon). This is the kind of crap that annoys people. Build up new characters then have them take over, people were happy to see Rhodes take on the mantle as they knew hiim and he'd earned it to them.