There is a "block" feature, it is called "mute" on hive.blog.
The blacklisting feature is actually less powerful: it doesn't block a user, it just puts a warning beside them. And be default, that warning is only going to show for the person doing the blacklisting. So it really doesn't matter if a new user blacklists someone, that warning will only show for them personally.
Oh I see. ok then...