There is nothing wrong with it’s policy.
Anyone can create a group and add their friends. Friends can opt out.
That simple formula will have two main impacts.
1. There will be more focussed groups, with respect to purpose and they will have the potential to be very intimate and private.
2. The current friendship system will be strengthened as people need to watch carefully who is in that circle, as any one of them could add them to groups they don’t wish to be in. Abusers will be unfriended.
Facebook is mediating trust not by policy but socially through it’s users.
Cyberspace is more like life, we will be more careful who we invite to the party, and have better parties, or business meetings for that matter.