From a larger perspective, there is no choice but to become sustainable. Our ability to use resources from around the globe increases the time it takes for natural limits to curb our growth. Holding back the natural limits through artificial means only increases the severity with which we will fall back to within those limits. I would rather see us consciously ease our way back into natural limits rather than wait until we hit disastrous natural balancing forces like decreased soil fertility or declining food species populations. Some types of exchanges are well tolerated even at high rates of population, consumption and waste production.
Breathing is a good example.
Many other limiting factors would come into play before human breathing would create significant problems. Other types of exchanges have significant impact even at low rates of population, consumption and waste production. Nuclear technology and genetic engineering are good examples of this. Most types of exchanges fall in between and their use must be evaluated accordingly. Resources, sources of input, can be classed by their availability over time.