The author fails to see that people exist in a reality where stuff like the Facebook Timeline is just another fact of life, and the facebook profile is just a useful component of getting to know someone. That is, I would imagine that most people are familiar enough with the mechanics of social networks to be capable of seeing beyond random old posts on Facebook when learning about a person.
Most people probably are, but most employers, lenders, governments, etc. (and malicious ex-SOs) can and do use any information they can get. Even if "it will never happen to me," guarding against the exceptional case of abuse is worth the effort.
