I didn't say anything about labelling, but facebook does have it in place. Its not just that they can't reply back; They can't even see their own comment or the OP any-more, let alone your reply.
EDIH: I agree with you that labelling is best and getting notified about something you can't reply to is stupid, but beyond that, I'm in favor of thinking of communities more as private spaces. Whether its right or not, mods, admins, blog authors or peertube videographers can treat those threads as if our comments are un-wanted trespassers and they have no obligation to explain their reasoning.
There's no point in getting worked-up about it. 99 times in a hundred, its not hard to anticipate how what we want to say will be recieved in a given space.
We aren't prisoners, so we are also free to choose to take our comments elsewhere, or start our own instances or communities to host them. That said, if you anticipate moderating the replies to what you have to say to be too much work, well, that's often how the mods in other places are looking at it.
Its often not just "letting you say what you want", but also, likely putting more effort into moderating the replies on your comment than yourself will have to. Work and effort you mostly won't see or acknowlege.
check my edit maybe