Something to consider, should you be able to see all the details of everyone's profiles when you aren't logged in? I could see arguments both ways.
SixLinks Developers' response:
Right now, our view is that work on SixLinks is public, so we don't want to confuse people with some private and some public sections. SixLinks isn't for private pictures of your kids, it's for collaboration on how to live sustainably.
Since everyone benefits from being able to see the conversation, we've headed toward an everything-is-public view. Post suggestions or comments if you disagree!