Landlord/employer thing you will have to pull an example as that seems unheard of and an invasion of privacy. Obviously don't have a beer bong in your profile picture, but they aren't going to grab your wrist and make you log in during the interview. Landlord has no business knowing anything about your life beyond whether or not you can pay rent.

All those other situations existed before facebook too, and people still got to reunions, went to church, and talked to their relatives living half a world away. Chances are, these people are signing into facebook with an email address or telephone number, so it's not like facebook is literally all they know unless grandson set up grandpas account (but I bet grandpa still has a landline, forwards nigerian prince emails, and writes letters just fine).