“Some of the issue here is the misconception that science fiction and fantasy fandoms have long been a preserve for straight white men when they have some of the most diverse fan bases of any genre. So some of the toxicity is definitely a small percentage of white straight male fans conflating mainstreaming with a forced diversification when that diversity has always been there. The bottom line is that these types of fans are used to being at the centre of these stories, and now that is shifting they likely feel a loss of power when, ironically, they remain privileged in almost all respects.”
As mentioned here and before, fandom in general has always been diverse, it's more so that due to social media presense and outlets, the world is becoming more aware of that diversity and while some cater to it, others deny it existed to begin with.