Earlier quoted context omitted.
I've moderated a forum before. Some people on the Internet are just crazy . If you ban them, they will come after you—maybe even in person. Shadowbanning on forums (setting aside the FB case) is sometimes abused, but it serves a vital purpose: preserving the time and safety of volunteer moderators.
Don't they just get twice as annoyed when they realize that not only were they banned, but they were silently banned and wasted time writing posts that went straight to /dev/null? The only time shadowbanning seems like a good solution is outright commercial spam and link farming, where slowing them down is a win in itself.
(I browse with showdead on because the volume is small on HN, and every now and again you come across people in the former category who were shadowbanned for one or a few incidents relatively far in the past, who since then seem to have acted reasonable, where it's worth pointing it out so they can appeal their ban - mostly the flagged comments or shadowbans are well deserved, though)