Note killfiles were per-user (they could be shared, but this was optional and required specific clients), so those blocked people were still visible for non-regulars.

The result was that newsgroups were very different for insiders vs outsiders: insiders saw nice clean message feed, outsiders saw tons of low-content messages with no replies and rare nugget of interesting info.

This was one of the big reasons why Usenet died for me: too much spam and useless messages, as there is no group-wide authority (and no, cancel bots never seemed to work)

Today, if you want heavily moderated group, there is plenty - they are simply scattered on the web. Many of them are phpbb-style forums, some discords and slacks (ugh...).