The "we're all a big family" narrative is a psychological ploy to try to exploit the need by most people to feel like they belong to some group. This need is deeply interwoven into our psyche. And as more traditional structures of society (extended family, churches, social clubs, etc) erode, it leaves a void that many cannot really understand. IMO, this particular message is almost never true.

Company "mission statements" and such are a similar tactic. Though I think it's a bit less cynical, because the company leadership sometimes (rarely IMO) believes in the mission to a minor degree.