What makes it toxic? Is it just full of people dunking on each other solely due to where they work?
Yes, that, as well as this weird culture to put your TC (total compensation - cash + stocks) at the end of your post so everyone knows how much money you make and people occasionally dunk on those who don’t make enough. There’s a large amount of sexism, racism, and transphobia floating around as well - just a byproduct of total anonymity. The only benefit is really the internal company discussions.
Not really a primary point of your post, but you might consider that recent history, and history in general, provide many examples where sexism, racism, and transphobia do not remotely depend on anonymity.
At least in the corporate sphere there is a large overlap between shitty people and those that don’t value privacy.