It really depends on the person because some people solely hate Jane because she is a woman, while others had their favorite characters taken out of the spotlight and are upset over that.
This is my view on people's dislike of Marvel's diversity push. Ex. people will rage for eternity over Iceman turning gay (not that his "outing" doesn't deserve to be mocked forever) but either don't care/actively like gay characters getting their own books like Midnighter and Batwoman. As another DC example, nobody gets upset at New Superman, Jessica, or Simon Baz while getting angry when a Marvel staple gets replaced by a brand new character. Of course the flipside is that DC's line-up is less diverse (I don't actually have the facts to back this up, but it seems pretty obvious) but they don't draw 1% of the ire Marvel does.
You also need to factor in the general angry racist/sexist nerd crowd i.e. people who don't actually read comics getting mad at diversity pushes. Marvel screams from the top of their lungs whenever a big diversity push happens so people react more strongly (if Marvel was releasing a solo book focused on a Lesbian it would be a big deal, meanwhile DC is like "yup, here's Batwoman"). I don't doubt that there are people attacking comic book writers on Twitter that don't actually know that the current Green Lanterns on the Justice League are a Latina and a Muslim.
This is just the opinion of a fairly new comics reader that is fine with diversity in comics and just wants good stories to read. Not calling out anyone in this thread (I don't think this has actually happened in this thread, more so in the OT) but I do think there's a tendency to call everyone on the opposing side a racist/sexist when there may be legitimate criticisms of a character being swapped for a new character who happens to be of a different race/gender. The thread about the rumor of Michelle = MJ in the new Spider-Man movie is a good example of this. (For the record, I actually want Michelle to be an original character because I think it would be interesting to see Peter with a new character after two movie series focusing on MJ and Gwen respectively).
Also I wanted to say that it's pretty funny thinking about how while Marvel is trying to create their own Wonder Woman (iconic woman hero) in Captain Marvel, DC is trying to create their own Black Panther (iconic black hero) in Cyborg. Only DC has kinda accepted that nobody will ever give a shit about Cyborg while Marvel will never stop pushing Captain Marvel.
