Shadow banning is a legitimate tool when you assume that it is necessary for you to offer your services with the absolute lowest barrier to entry. There are plenty of other very reasonable approaches to prevent malicious actors from simply creating new accounts - the easiest of these is to attach a modest cost to account creation which is a solution that marketers absolutely loathe band thus has been casually discounted. However, it is an exceptionally good solution.
Do you think twitter would be dealing with 10 million twitter bots if they had a five dollar account creation fee? Do you think smurf accounts for harassment would be nearly as widespread if every ban cost the troll $5 of their real money?
Yup - I'm well aware - and the barrier to entry for HN is pretty much non-existent. Some features are locked behind karma accumulation but most of the moderation is done manually and the community is small(ish) enough and of a professional bent - meaning that a lot of people know who other folks are IRL. Removing the anonymous factor for a large portion of commenters makes them follow the rules a lot better.
There still are lots of issues with smurf accounts though, again, there's a sort of barrier to entry in that extremely new and low karma accounts can get their comments [dead]'d very trivially.
Do you think twitter would be dealing with 10 million twitter bots if they had a five dollar account creation fee? Do you think smurf accounts for harassment would be nearly as widespread if every ban cost the troll $5 of their real money?