Mmm. I'd agree it would not be desirable, but why do you think it will be an option? Not being a smartass here, I'd just would like to be more optimistic than my current knowledge permits. We have ~ 75million net global population increase every year, every one of whom wants to have the std of living of a upper median income US life style ( at least ). Sorry, but I don't see any reason to think that our current life style together with the current and future population is sustainable. Something has to give.