All too often, in today's greenspeak parlance, "sustainable" means subsidized. It doesn't have to be, but it has been and continues to be the most disingenuous and egregious of eco-jargon patois passed-off as earth-friendly by the progressive non-profits , corporatists, and other rent-seekers of the left. All of the HOV pomposity of the planet-savers and the LEED certified architects at their conventions can't make it otherwise, despite all of their earnest declaiming and seriousness of purpose.
Here's the reality: if a green system, concept, product or energy solution is being offered as "sustainable", and its use therefore imperative, it should be assumed unless it can be demonstrated otherwise, that there is a government subsidy embedded somewhere within it to propagate it. It might be a mandate, it might have its production or labor costs underwritten, its competition may be abolished or selectively taxed, or perhaps some level of government is its primary customer. If any system or concept or energy solution is being referred to as "unsustainable", then, almost invariably, it is privately financed, already, or about to come under government oversight, and probably involves hunting, mining, drilling, manufacturing, cropping or fishing, in one form or another in exchange for money at market prices. The trendier opponents of such "unsustainable" activities will tend toward, or even fully embrace, the beliefs that carbon dioxide is a pollutant and a poison and contraception is "the cheapest way" to combat "global warming". Doomsday is right around the corner.
Rent-seekers are completely predictable (and sought after) by government bureaucracies, and their goals are therefore "sustainable". They are the segment of society the bureaucrat can most readily plan for--and measure. Instead, the entrepreneurs, the wildcatters, the venture capitalists, the innovative production farmers and independent inventors of all stripes, who, by engaging in risk-taking endeavors beyond legislative imagination create and maintain with their hard work and incremental improvements the technical and theoretical bases of all advances in civilization, these are the "unsustainable" ones: yet they are as indispensable as they are incommensurate. These are the people who have no need to fill in the endless and intricate government grant and assistance forms that keep the union bureaucrats at their desks working so diligently day-in and day-out. They ask for nothing more than an opportunity and a marketplace. In a politically-driven economy such behavior is discouraged to the point of being unsustainable.