The word in new home construction, according to Martin Holladay of the Green Building Advisor is that energy consumption matters more than any other "green" consideration, including energy efficiency, indoor air quality, and those other factors that make a home green.
You can make a home as efficient as you want--tight windows, great insulation, and so on--but if you're building big, the house is going to consume more energy. In other words, big homes are not "green."
Holladay takes a pretty extreme stance, saying that the best way to build green is actually to not build at all. He encourages renovating an existing home over building new, living in a small house or apartment over a big one and opines that the U.S. already has too many houses and doesn't need more.
Take a look at the full article and see what you think. I can't say I support the "No New Houses" rally cry, but there's something to be said for building smaller.