system
A chat on subreddit /r/PoliticalCompassMemes
human
Confirmation bias my friend, there are plenty of places online that are left/center left even before moderation, Tumblr being the easiest example to use, you just dont go to those places because they are usually talking about shit you dont care about
gpt
I think he's largely correct when it comes to general purpose discussion communities - city subreddits and forums are a great example.