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But you can be banned from sub A if you post in sub B because mods from sub A don't like sub B, even if what you posted was something that mods from sub A would like... and AFAIK you won't find out you were banned from sub A until you try to post on sub A. Not that it happened to me, but I've seen plenty of cases.

On most forums there's no automated system that automatically shadowbans users for using a blacklisted IP.

They also don't quietly remove comments in a way that is invisible to a user for triggering some keyword in AutoModerator or a spam filter. And there are usually no minimum karma or account age requirements for posters.

> On most forums there's no automated system that automatically shadowbans users for using a blacklisted IP.

Any large site does this. Even HN.

Some of the moderators ban anyone anyone who makes comments that they do not like, even if comments are reasonable, polite, and within rules.

Moderation of that type usually seems to be secret, but the problematic moderators that I have noticed seem to be trying to protect some political belief or pet disinformation from discussion. It poisons the entire site for me.