What identity crisis?

Earl Mardle has a great post today on identity from which this:

Despite all the panic and performance that goes on around privacy and stalking and authenticity online, I don't think we are necessarily doing anything new. Throughout our lives we establish relationships with strangers. We meet somewhere, we exchange "identities" that are no more reliable than any online pseudonym or avatar, we exchange opportunities for trust to develop and we form relationships. But those "real world" relationships are no more real than many online connections.

Think of all the mass murderers, urban terrorists, traffickers in god knows what; how do we say, "oh my god how could it be, they were such nice people, quiet, unassuming, generous, pillars of the community. I would never have suspected that." How often do we say, the spouse is the last to know. Been there, done that, from both sides. So who IS this person with whom you share your life again? What IS their identity?