I believe in using the most natural materials with the least deleterious effects not only to the occupants of the home, but to the occupants of the rest of the world as well.
The sun dried mud bricks of my 110 year old adobe home have much better thermal and elastic performance than concrete while embodying less than a tenth of the energy.
Ask the hard questions and don't accept "cause that's the way we've always done it" as an answer.
For more information:
Read "What materials should I use to build an eco friendly home?" a Q&A answered by Polly Osborne.