I think many of the latest incarnations of so-called new urbanism give it a bad rap. Often, they do seem to be trumped-up (if not Trumped-up) gated communities, which encourage people to be insular as Amerabizarro suggests. New urbanism as it was originally conceived is meant to create real community like you see in centuries-old European cities (and, of course, Manhattan). That just means that the stuff you really need is easily accessible and doesn't require use of a car. Reducing car use helps generate a sense of community by making outdoor spaces more inviting and encouraging people to engage one another (not to mention the environmental benefits).
Diversity and inclusion is another basic tenet of new urbanism, I believe, but this is the one most often flouted by planners under pressure to keep property values up.
My view is that one of the best ways to improve neighborhoods is to invest in non-car modes of transport - including public transport and cycling infrastructure.