Where the bias isn’t obvious until you spend time on them.
The first examples I can think of are r/Canada and r/WorldNews
Everywhere has bias, you can’t escape it. Whatever happened to don’t believe what you see on the internet.
I see your concern for truth in any scenario, and I agree validity should be a constant consideration! However, bias and astroturfing are different. Bias is the lens that we use to look at reality. Astroturfing is forcing lenses onto many others without them knowing. It is a deliberate campaign.