Forcible silencing of opposing views is a central tenant of actual fascism (not the kind of "fascism" that kids on social media accuse people of just for disagreeing with them).
History repeats itself, it would seem. This is a modern day book burning.
The common factor is authoritarianism. Zizek makes a difference in that the left always consider the offender as just brainwashed and potentially redeemable (hence, siberia work prisons) versus the right as irredeemable and non human (hence, death camps).
The exception is the case where a US government entity controls an account that is a mod of a subreddit, in which case they would be subject to the First Amendment when performing mod duties such as deleting user comments or banning users. This specific case would burden only that user and would not place any additional burden upon the non-government mods or upon Reddit itself or its admins.
However, that does not mean we should not criticize reddit for not standing up for freedom of speech. You can't make your whole website based around "open and honest discussion" then ban subreddits where open and honest discussion was happening, but in ways you didn't like.