There you raise an excellent point which enables us to relate Facebook back to the real world where I think our intuitions and laws are better. Suppose a plain

There you raise an excellent point which enables us to relate Facebook back to the real world where I think our intuitions and laws are better. Suppose a plain-clothes USCIS agent comes to find you in a place you are likely to be and chats to you - say in a bar, or your place of work. Is anything they discover during that chat admissible, even if they don't admit to being a USCIS agent? Because if that is okay, then why should a social network be any different? On the other hand, if that would be inadmissible, or require some evidence beforehand for them to mount such an undercover operation, then viewing your private online data under the pretext of friendship should be out too.