That would be because A) this thread diverged from that when the assertion that all shadowbanning ain any forum is harmful to the community, and B) as noted elsewhere in this discussion, FB isn't shadowbanning, they're denying sends and a UI bug later is removing the information that the send failed.
> Where’s the default option turned on on HN?
I'm not sure what you're asking. If you're asking if showdead is on by default on HN, no, it's not, and I don't think it should be.
The whole point is to make it so people that are not contributing usefully to, or worse are actively harmful to, the discussion and community are less likely to cause a disturbance. Any one of those people can easily tell if they are shadowbanned if they decide to check just by opening up an anonymous browsing instance and looking at the same discussion. They then have the option of either trying to contact the moderators to make a case, continuing on and trying to align better with the community in future comments and hope someone vouches for them (if they're aware of that), or making a new account and starting over.
But, ultimately, even if they don't even know they're shadowbanned, as long as they try to align their behavior with the community, I think there's a good chance they're be vouched for enough to not be shadowbanned after a while. When that doesn't happen, from what I've seen it's because they haven't really made an effort to change. For example, a dead user fit2rule posted yesterday about how they've been dead for a few months. I looked at their comment history, and the vast majority of them are single line responses. Those aren't necessarily bad, but they probably don't cross a threshold to make people decide they contribute enough to vouch for them. At the same time, the occasional comment they have with more than a sentence that seems to try to actually engage often doesn't show as dead, as someone must have vouched for it because they though it was worth being expressed. If they had kept with that type of engagement, I think they would not be dead at this time.