I’ve been asked a couple of times why it is that my status posts on Facebook are locked down, visible only to friends or sometimes friends-of-friends:

…but yet with the same button-click that I post to Facebook, I post exactly the same thing, publicly, on Twitter:

Surely that’s undoing all the good of my Facebook privacy settings?

The reason is because I’m not doing it for reasons of my privacy – I’m doing it for yours, and what your expectations of privacy might be.

On Twitter, a reply to me is a first-class citizen – a tweet in its own right. It has a ‘reply ID’ field to help thread conversations, and it mentions my handle using the ‘@’ convention, but otherwise it is a tweet like any other. You, the replier, have one simple privacy setting – is your account public or private? Can the world see your tweets (including that reply) or just the people you allow?

By contrast, on Facebook, a comment is a second-class citizen – a child of the original post. Implicit in this is that it inherits the original post’s privacy settings. As the commenter, you do not have control over who sees what you write. Assuming – as most have – that the original poster has accepted the default privacy options, the commenter has only one choice: either allow their reply to be public and searchable for the entire internet, or don’t reply.

On Facebook there’s no way I can let you set who can see your comments, so I do the best thing I can: make your comments visible only to the 300 or so people who I am reasonably sure are not evil. If you like, you can check the list and see if you object to anybody on it.

It’s not ideal, but it’s the best I can do to respect commenters’ privacy on a service that itself respects privacy only grudgingly.