"You have one identity. The days of you having a different image for your work friends or co-workers and for the other people you know are probably coming to an end pretty quickly … Having two identities for yourself is an example of a lack of integrity."
It's not a lack of integrity - what people say and how people act is always based on the context it's in. There are things you'd say to your friends that you wouldn't say to your family or even other friends. It's always been this way, and it's pretty arrogant for Mark and, consequently, Facebook to assume otherwise.
This has actually pretty much pushed me off Facebook, as the only stuff I post is what falls in the relatively small subset of stuff I'd tell to my family, coworkers, boss, friends, and people that I know online.