A discussion we have in comments will be open to people other than the two of us. People who read the post and are thinking along similar lines can see our back-and-forth. The comments will be attached to the post, potentially clarifying things for people who come across the post later. If the question comes up again I can link someone to our discussion of it. The comments show up in search engines for unrelated people interested in these ideas. Since communicating in public has all these positive externalities, I'm much more willing to put time and thought into a discussion if it can be public.

There are also benefits during the discussion, as other people often have valuable things to add. Many times a comment thread has been me and someone else, and a third person jumps in with an important consideration that hadn't occurred to either of us. Other times someone's comment sparks a thread which brings in perspectives from many people. It's not just that our talking in public helps others, but it helps us too.

More selfishly, comments have different expectations around responses. I read every comment, but I often don't reply. Maybe the comment is self contained, and while it's communicating something important a reply wouldn't add anything. Maybe I'm not sure how I'd like to respond yet, and then don't end up coming back to it. Maybe other people responded and it seems like the important details have come out already. Maybe I just don't have time. With one-on-one messages, however, the response burden is much higher. Just writing back "received and read" would be hostile, but writing a good response can be a lot of work. Sending a message should not generally obligate a reply, but it still feels rude not to put in the time for a thorough response.

There are valid reasons for non-public communication. Perhaps you're afraid of how people might respond to revealing details of your identity or taking an unpopular position. Perhaps you want to talk about something that is illegal but generally viewed as ok among your friends. Perhaps there are people who follow you around the internet harassing you. Perhaps you don't trust yourself to phrase sensitive issues in a way that doesn't lead to people being mad at you. This is not an exhaustive list! Private messages I've gotten about posts, however, don't seem to be sent for one of these reasons. If you're sending a message privately for a reason, it's helpful if you can say so.

While I don't normally ask for emails in response to posts, this particular one seems like it should be an exception, so you're welcome to write me at jeff@jefftk.com. I'm not committing to reply, though!