I agree with you that facebook is a useful tool for us to stay in touch with family and friends.
However, I would say most folks use facebook as a way to say “Hey, look at me.”
I also think facebook can be very dangerous.
Just about anything can be turned to dangerous use. FB is not going to be fail-safe, but it can be safe if used discreetly and wisely. Some make mistakes and post things they really should regret and many resent being corrected (even in private mail), but that’s par for the course. It becomes a public square and with the right community one which is simply an extended version of your local community center.