I don't think anyone ever claimed that no fans were racist or sexist, in the past or currently.
Yes, they have. It's the go-to response of the racists and sexists whenever someone pushes back against them. We've seen it with every Star Wars project that was attacked on the basis of having women and minorities in prominent roles, and it's continuing now with The Acolyte. And that's just looking at Star Wars.
There are certainly terrible people out there. The claim is that big-budget heavily advertised movies don't fail because of racists or sexists, they most likely fail because they aren't good, and movie studios use diversity cynically to give themselves a scapegoat in case their movie bombs.
Every movie that has failed - whether financially, critically or both - has failed for a variety of reasons (and plenty of well-received movies didn't make money, while a number of movies with a mixed or negative reaction made bank. See most films made by Michael Bay). But it's only when a movie starring a diverse cast and helmed by a diverse crew fails that the blame placed mostly or entirely on the women, racial minorities or LGBT people that were involved. The bigots who will claim they aren't bigoted will continue to yell "Go Woke, Go Broke" every time a diverse movie fails and pretend the diverse movies that didn't fail weren't diverse - that is, when they don't also claim the studio faked box office numbers like they did for Captain Marvel.
I don't know if these studios are using marginalized groups to give themselves a scapegoat but it's not like the anti-woke crowd aren't happy to scapegoat said marginalized groups when a film or show bombs. As they are doing, again, with the latest Star Wars media that they got pissed off at before it even aired. To the point of review bombing
a movie that had a similar name to the show.