Reddit has fallen to this same problem with subreddit moderators. A subreddit moderator can remove posts and comments they don't want anyone to see.
A lot of the popular subreddits and many of the more obscure subreddits are moderator-crafted echo chambers. Some moderators have unbelievable amounts of free time to observe the subreddit and surgically remove discussions they disagree with.
Worse, it's all invisible. These subreddits become an extension of what the moderators want without the moderators having to show their actions at all. When you visit a subreddit, you could be reading a carefully constructed echo chamber of a single moderator and have no idea.
I think the Reddit situation would be very different if it had a "showdead" style option that let readers see removed comments.