Sure, but when I’m replying to someone in any context I’m responding to that person and what they said. It being a public forum just means new lines of discussion with other individuals can offshoot from a single comment, with an added layer of public opinion in the form of upvotes and downvotes. Unless explicitly stated, the only posts that I perceive as speaking to the forum as a whole are original posts and oftentimes top level comments on those posts.