Believing you are morally entitled to reply directly to someone because they speak in public is…definitely a position, I guess, but I think being able to specify how you want to be interacted with is deeply humane. (And being able to do it after a thread starts to go sour is so important.)
Someone will ask why blocking doesn’t make this unnecessary and the short answer is that prevention is better than picking off unwanted interactions one by one, and having to process each one as you do it.
Someone else will say that if you don’t want everyone to be able to say whatever they want in your thread whenever they want to say it, you shouldn’t post in public because that’s the bargain.
But like…I don’t want the old bargain. The old bargain is kind of shit! We have a million ways to contain and shelter even “public” conversations offline, let’s have that in the good online places, too.