When I go to a store in "public" like Walmart, and buy a bottle of whiskey, an onion, and a deodorant, in front of hundreds of strangers, sharing willfully my payment details with Walmart and Visa, when I get home I still do not expect all my Facebook friends to know what I bought, to have pictures of me buying the items and to have a copy of my receipt. And some of them even have Walmart as a friend. Some even Visa!

Yet all is public information and happened in a location with no expectation of privacy.