The whole idea behind “not sustainable” is that it is not possible to sustain something.

-1 That is not "the idea!", that is the definition. A recursive one at that.
-2 That doesn't really follow from either your or OPs comments. What is not sustainable? The economy, society, global trade? Did you delete a sentence?

I think your comment makes more sense if I was arguing for people to counteract population decline. I am not. I was simply pointing out that it won't be sunshine and rainbows as OP and many commenters here seem to believe.