Almost all sociologists and anthropologists agree that humans can't keep track of more than 150 people. That's pretty much the upper limit of a Stone Age society.
In modern society, we fill up a lot of those spots with celebrities, which makes our everyday neighbours even less likely to make a significant impression (unless they really annoy us).
There have been a lot of social studies done showing that if people know that other people are keeping track of them, they are more likely to play by the rules, be polite and show compassion. This is the justification behind slut-shaming and rude-busting and the other share-and-shame postings on the Internet.
But there's another side to the 150.
Someone can post a photo of a car running a red light and the Internet can marvel and finger-point and name-call to their hearts' content.
But if we were really part of a village-group, it wouldn't just be the shamed who would be known. The shamers would also know and be known. So they would know if the car belonged to Mr. B, who's really a sweet guy but absent-minded (maybe look at taking away his licence or arranging for someone to run his errands) or Ms. R, who is nasty and self-centered and deserves some time in the place of public shame.
When it comes to judging other parents, this becomes even more critical. Amy Alkon, in her book I See Rude People, encourages people to reprimand other people's children if the parents aren't doing their jobs. I have a problem with this.
First, the majority of parents are doing their jobs. Children aren't 100% controllable but the majority of those I see out and about are well-behaved.
Second, outside observers don't know if there's something behind the behaviour other than "bad" parenting. A child with autism doesn't have a physical symptom to warn observers, neither do kids with ADD or deafness or any other number of challenges.
My children have been reprimanded by adults. A lawn care guy was trying to convince me to sign up, accidentally knocked over his clipboard and Nathan laughed. He yelled at him. (Needless to say, I did not sign up for services.) There have been three separate times where an adult has tried to physically discipline Alex. I've lost count of the number of dirty looks and screaming sessions I've been subject to.
I was taught that successful social interaction meant that no one ever thought of you with anything other than pleasant memories. I'm now more onto a train of thought which says other people's reactions do not outweigh my children's right to dignity and respect. Which means they do not deserve to be cursed at, yelled at, scowled at or physically disciplined by the general public. They have a right to be in public and shouldn't be expected to be invisible and inaudible.
I'm willing to bet that when we were still in groups of 150 or less, more people understood that basic principle.