Community units were a carryover from when we had villages which were essentially the same thing in function.
Your family, your community and your social network are three different things. Your family are the people you're born with, your community are the people you cooperate with to survive and the social network are the people you associate with voluntarily both inside and outside the community.
After we lost the community unit to suburbanization, there was a huge spike in murders because serial killers could rampage freely. They could do it because people were so isolated that they didn't know who could be doing it. Serial killers started going back down again when we perfected DNA evidence and they started getting caught.