Consider, first, that reduced resource use and sustainable lifestyles, on both the cultural and the individual level, need not mean deprivation.
As an individual-level example, studies show that bicycle commuters are happier than car and transit commuters. As a cultural-level example, people who live in pedestrian-friendly areas like villages, where cars are used less frequently, tend to have more friends, the research shows.
In both cases--how a person chooses to travel and how a culture develops its land--the scenario that uses fewer resources results in better quality of life. The happiness of people, therefore, does not depend on energy and material use. It depends upon whether materials and energy are used effectively to improve well-being.
Perhaps the designer of truly sustainable products and systems must ask, therefore, not just whether the product or system has the lowest possible energy and materials input. Perhaps the designer must also ask whether use of those valuable ecological resources can be justified in terms of quality of life improvement.
In other words, as I'm defining it, the "environmental effectiveness" (E) of a product or system might be mathematically represented by an equation that looks something like:
E = life enhancement / ecological resource use.
The more life enhancement (pleasure, health, contentment, security, community, connectedness) delivered per unit of resource, the higher the environmental effectiveness, the more sustainable the product. In other words, even a conventionally-grown apple has a higher environmental effectiveness than organically-grown tobacco.
And if you think about it, products like sugary sodas, when they contribute to childhood obesity, wouldn't score so well either. Carrot juice, on the other hand, even in the same throwaway container, even using the same resources to produce, because it delivers important nutrients, would score better.
Why is life enhancement so important in evaluating sustainability? Because we have become so short on environmental resources that we can no longer afford to be wasting them on things that don't even improve our lives.