> "When communities grow to a certain size, people no longer expect to interact in the future, and thus are more likely to defect – to be petty, mean, aggressive..."

Wow. I can't say whether this is true or not, but how depressing. Instead of counting on this behaviour, what if we tried to change it? Kindness, respect, and general "give the other person the benefit of the doubt" attitudes could make a huge difference. I just can't get around the idea that not interacting with the same person means you can not care how you treat them... that's crazy.