But its not your next door neighbour. There's a whole system in place to make sure it's not your next door neighbour, and in fact we generally accept as a society that preventing people's social groups gathering information on each other largely solves problems with privacy (provided we also don't allow people to rebroadcast things as they please).
How much do you care about the credit card purchases of someone you've never met, who lives on the other side of the country, and who you wouldn't recognize the face off if you saw them? How much of your internet posting is done on the exact same assumption?
Well, if you live in the Washington DC area, the chance substantially increases. ;-)
Though, if you have ever been in a position to gain a glimpse into strangers' behavior, be it what bars/pubs they frequent, how they make income on the side, what stocks they trade, or any number of not widely publicized tricks-of-a-trade, I can guarantee you that you would use that knowledge for your own gain and/or entertainment. Your use of that information is untraceable, and in the very worst case can be plausibly denied.
But it's not untraceable. There's a reason the LOVEINT cases at the NSA were found: because the NSA goes looking for them in a pretty draconian way.
The technical capability to do something doesn't mean you have the legal capability to use it or broadcast it and a good deal of your post is starting to hint at quasi-illegal activity in the first place.
How much do you care about the credit card purchases of someone you've never met, who lives on the other side of the country, and who you wouldn't recognize the face off if you saw them? How much of your internet posting is done on the exact same assumption?