So, I don't know, but it seems to me that if someone toots something public, it should be ok to reply to it, unless that very toot requests no replies. Even then it would seem odd to me.

I know that others feel differently. I just don't get it. In particular how are we supposed to know when we can and when we can't?

Is this a conversation medium, or just a publishing medium? If the latter, why is there a reply button?

Reply to this or don't, as you wish.