Facebook has taken a lot of flack for an aggressive, “opt-out” strategy around some of its products — specifically, the fact that your Facebook friends can tag you in Photos without your permission, and that they can now add you to Groups without your permission. Chief executive Mark Zuckerberg described some of the thinking behind that approach on-stage today at the Web 2.0 Summit.

The social networking company credits this design with fueling the rapid growth of Photos (which is now the most popular photo-sharing application on the Web) and Groups (which Zuckerberg called one of Facebook’s fastest-growing products ever). But this approach can lead to some awkward situations, like when a friend tags you in an embarrassing photo or ropes you into an inappropriate group.

Zuckerberg pointed out that you can just un-tag the photo or leave the group. Interviewer John Battelle described that approach as one that “doesn’t ask for permission, it asks for forgiveness.”

“The friend relationship is manual,” Zuckerberg replied. In other words, Facebook asks for permission before you approve someone as your friend, and that permission gives them “the right to do certain things.” The implicit solution: If you don’t like what a friend is doing, then you should un-friend them.

That was basically my response to the Groups complaints, but it will be harder for Facebook users who approve any and every friend request that comes in. So this seems like another way in which the company is designing its services so that Facebook connections reflect real-world connections, rather than a willy-nilly approach to random friend acceptance.

You can see that in yesterday’s launch of a new version of Facebook Messages. One of the reporters at the press conference noted that by prioritizing any message sent by a Facebook friend, the company seemed to be discouraging people from making new friends on Facebook. Director of engineering Andrew Bosworth responded: Yep, pretty much.

“I don’t think the goal of Facebook was ever to expand the social graph,” Bosworth said.

[photo by Dean Takahashi]