How (racist/sexist/whatever) harassment on Mastodon works:

1. Harasser replies to their target's post, with the reply set to "followers only", saying the most vile stuff you can imagine.

2. All the harasser's followers join in on the harassment, posting more vile stuff.

3. Nobody but the target and the harassment crew can see the vile stuff that was said.

4. Target is traumatized. Nobody else can see why.

5. Everybody says "I don't see it so it's not happening."

https://community.hachyderm.io/blog/2024/08/12/hachyderms-introduction-to-mastodon-moderation-part-1/

Hachyderm's Introduction to Mastodon Moderation: Part 1

The first post in a series about Mastodon moderation tooling. This post focuses on context for the upcoming posts.

Hachyderm Community

@dave
This is why hiding content (either from blocks, lists, etc) has so many trolling edge cases.

...Which leads me to wonder: What is the reply's visibility being able to be set that supposed to do? What is the intended use case? Why can a replier or quoter be allowed to isolate someone like that? Is it hidden from moderators?

Replies are just posts, and all posts use the same security options (currently). The feature is there so you can have an OP that is only visible to followers. Lots of people do that to keep their posts among friends, basically. The core issue is that because servers are federated, every post has to carry the privacy level with it, letting it be switched mid-stream.
@dave Could there be a moderation setting where I could choose not to see any posts that are followers only if I am not following the person who authored it? Even if it mentions me by name? But still see public posts that mention me by name.?