I have been on reddit for just about 12 years now. Something I've noticed over time is just how hateful the place has become. A complete outrage machine. Every single sub became filled with it. I've filtered so many subreddits over the last few years, it's insane. I don't know enough about this place to be sure, but I do hope it doesn't become the same type of echo chamber of anger.
Zizek is a sexpest obsessed with comparing everything to rape and his followers are a cult of personality. This is a very strange one to include in your list of non-echo chambers, particularly as he and his audience are political partisans just like the first three you criticised.
The inclusion here seems more like snifffff ideeeology, as he would say.