We like to create neat, silo-ed, identities.
On Facebook, we create identities to impress those we've met in the past.
We create an idealised life for our friends and families. Bad photos are removed, good photos are kept. We share pictures of our vacations for others to admire.
In a community, we create identities that help establish our positive distinctiveness among that peer group. That often means establishing our credentials. Those credentials might be geeky enough, smart enough, experienced enough etc…
Take this profile on SK-Gaming by my former gaming colleague 'Zechs'.
The same credentials that he amplifies to help him achieve a positive distinctiveness among the gaming crowd are the very same that would be embarrassing if he posted them on Facebook (or in other areas of his life e.g. work).
Having our unique identities overlap is a big concern of your members. We don't want the risk of social ridicule (or even rejection).
This is why HuffingtonPost's announcement to link every comment to an identifiable Facebook account is causing outrage. HuffingtonPost doesn't force comments shared on the site to appear on Facebook, yet the slightest whiff of a link between the two is a cause for concern.
Not many things have the potential to destroy a community overnight. But this might just do it.