Why sustain?

If everything could be designed to be ‘truly sustainable.’ I.e. harmonious with nature- derived almost directly from nature or imitating it, creates no waste, not specific to market, inter-generational, inter-cultural, plus all the other crazy stuff that comes under these headings such as ‘self-repairing,’ perhaps, ‘emotionally durable.’ etc. etc. etc. you know what I’m getting at.

My question is, what then? Why all this progress? Why do we want to ‘save the Earth’? Why do we need to live longer, if there are already too many people? What happens if we live forever or extremely (by today’s standards) long times- how can we be ‘considerate’ of the next generations? How do we prevent the next generations from making the wrong moves? Are we evolving as people?

Ok… that’s too many heavy questions to ask at once (perhaps we need a ‘design philosophy’ thread or board to ask this kind of stuff). But it basically comes down to why progress and what’s the purpose? Theism aside, why do designers take it upon themselves to ensure this progress?