For the record, we've been discussing making this post for about a week. The fact that it was brought up on the site recently in a practical way was just good timing. While I am torn on the idea of being able to block someone from being able to reply to my comments in other people's posts, I do recognize that it could prevent someone from trolling me. Right now we don't see this often, but it could become a problem.
Wow, talk about coincidence. It's ridiculous of course to hope that harassment and stalking just "won't happen" on hubski. There would be some workarounds for those who wanted to reply to a person in a thread but couldnt; they could reply to the thread itself (as long as it wasn't also posted by the person) and then do a call out to a user, unless call outs of blocked users are also disallowed.
I get legit throwaway hate-comments from time to time. That's the internet. It happens. I even occasionally wish I could reply in discussions where I'm muted - that's the point. I've got a sock ready-made if I wanted to use it; not the point. That's one of the best things about this place: the social engineering functions in such a way that it encourages human discourse.