I am all for working for sustainability, but for sustainability you must begin where it is at least possible to be sustainable. At 6.6 billion people with the concomitant environmental destruction, we are ... how far away from a population sustainable on the remaining ecology?

4.5 billion too far? 5.5? 6.5?

"If there were one species that could disappear for the benefit of the sustainability of the planet, it would be us." -- Jane Goodall, "The Selfish Green" BBC debate

Yep. As always, population is one of the primary problems. I think our cultural/belief biases regarding growth and our rights to reproduce are so strong that it will take non-voluntary reductions to shake us (as a society) out of our complacency.