Censorship takes a lot of different forms imo. Self-censorship usually takes place because one or more other forms of censorship are already at play.

There's authority based censorship, like the banned books list. People legitimately believed that Catcher in the Rye caused serial killers at one point and definitely cast judgement on those willing to admit they'd read it. At the time, reading the book could cost you in social capital which I think is what PG is alluding to. From what I read, PG just wishes we didn't exercise moral judgement - which I get. I came from a religious background that weaponized their morals for ostracization or for hate, meanwhile, nobody within the system recognized they were doing that because they were blinded by the righteousness of their morals. In that way, morals are sticky webs.

My curiosity drifts in a different way - assuming you can't rid the world of moral addiction - why were the people who believe such foolish morals (like banning books) not punished post facto? Folks with a laundry list of morals will often use the word "consequences", but where are their consequences when this moral falls out of style and has senselessly ruined lives?