Privacy is born from respect between entities. Considering the concept in the immediate sense, there is little need for privacy. In small communities, there is effectively none. In larger communities, it is conferred de-facto through anonymity.
A group of close friends or a family unit are about the smallest definition of community available. It's here the rationales and bounds for anonymity start to unravel. The argument for withholding information of "not your business" crumbles. But assuming a healthy and reciprocal relationship, in quantities of near direct proportion to the loss of privacy an increase in respect is found.
If push came to shove, invading the privacy of your closest relations would be a trivial task. This fact is demonstrated regularly in the events following a death. I assume it's not regularly performed because of counter-balance of respect.
Which leaves me to ponder personally relevant situations acting as counter-examples to my theory...
The cracker identity exists to obtain illicit access to information - invading privacy. Does this imply crackers do not generally respect society?
I cannot conceive of a mother whom, given the opportunity, would pass on invading their child's privacy. Does this imply mothers do not generally respect their progeny?
The corporate world expends billions of dollars into analyzing publicly available information about individuals. The hoped for result to the possession of valuable private information to leverage. Does this imply businesses do not generally respect their competitors? Or their customers?
Perhaps, samfu, this all comes back to spitting in the soup.