As a former mod of /r/politics the reality is quite mundane. The bias you see on the front page of that subreddit is pretty much entirely due to the users upvot

As a former mod of /r/politics the reality is quite mundane. The bias you see on the front page of that subreddit is pretty much entirely due to the users upvoting. The mod team is really careful to ensure nothing gets removed simply due to political differences and is internally transparent, and includes mods from a wide spectrum of political beliefs and backgrounds. Interestingly the mod team is simultaneously accused of being biased towards left and right wing politics at once!