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?