Pardon my being naive, but I find it amazing how exchanges on StackExchange are always so high-level and civil. I know very little about StackExchange itself, h

Pardon my being naive, but I find it amazing how exchanges on StackExchange are always so high-level and civil. I know very little about StackExchange itself, how have they achieved that kind of quality? As a follow-up question, why are all communities not doing the same?