I really couldn't care less about carbon footprint, and neither does the majority of the New Urbanism's target market. Successful NU projects have taken advantage of wealthy suburbanites desire for a lifestyle change, not an environmental crusade. One of the best parts about the NU is that it creates urban places that appeal to middle-class, middle-aged, (maybe even - gasp) Republicans. I hope the CNU never loses sight of that fact.
The notion of a "carbon footprint" when presented in the abstract is pretty meaningless, but it becomes much more relevant when you think about the effects of that footprint on our medium to long term quality of life. I think the video does a good job of explaining that sprawl fails not just as a quality of life approach, but also as a question of a sustainable society. More sprawl just won't work. In less than a hundred years we've eaten up huge amounts of land, nearly ruined our water supply and killed off hundreds of animal species. That doesn't sound like a long term plan to me. I think we either change our approach, a la New Urbanism, or we burn the candle at both ends until there just isn't anything left.