I always think of things I should have added in the hour after making a post. Sigh. Here goes…
The situation is perhaps not so different from mailing lists, Google groups or any number of similar systems. I can set up one of those and add people to them without their consent — even people who are are not my friends. Even people whom I don’t know and who don’t know me. Such email-oriented lists can also have public membership lists. The only check on this is that most mailing lists frameworks send a notice to people being added informing them of the action. But many frameworks allow the list owner to suppress such notifications.
But still, Facebook seems different, based on the how the rest of it is configured and on how people use it. I believe that a common expectation would be that if you are listed as a member of an open or private group, that you are a willing member.
When you get a notification that you are now a member of the Facebook group Crazy people who smell bad, you can leave the group immediately. llBut we have Facebook friends, many of them in fact, who only check in once a month or even less frequently. Notifications of their being added to a group will probably be missed.
Facebook should fix this by requiring that anyone added to a group confirm that they want to be in the group before they become members. After fixing it, there’s lots more that can be done to make Facebook groups a powerful way for assured information sharing.