Kaid Benfield writes a blog called Switchboard which is affiliated with the Natural Resources Defense Council (NRDC).
This is the essence of what he says in a new post called "The environmental paradox of smart growth":
There is no question that sustainable land use requires, among other things, neighborhood density. Indeed, I have basically staked my career on the proposition that we must increase the average density of our new (and, in some cases, existing) built environment in the US if we are to achieve anything near sustainability as we absorb more growth. Nothing has been worse for our environment than sprawl. Smart growth based on walkable neighborhoods, transportation choices, nearby amenities and the accommodation of an increasingly diverse society – more urbanism, if you will – is the only way we can limit per-capita impacts, and thus total impacts, to a manageable level.
But we also must be honest with ourselves about something, if we are to get this right: Environmental impacts will occur with development; to limit them, we must concentrate them, and this can mean increasing them in some places. This is what I call the environmental paradox of smart growth. Only if we understand the paradox can we address it. Only if we address it can we really create better places in which to live, work, and play – and surely that, not just lowering pollution numbers, must be our real goal.
I agree completely. This is so well said that I am honestly taken aback. I really urge you to follow the link above and read this post in full. It'll repay the effort, and it isn't that long.