you don't get to back out of providing evidence just because the situation is a hypothetical.

I use the word "evidence" to mean empirical evidence, that is, evidence from reality. Such does not exist in this case. Arguments from analogy, logic, etc. are not evidence.

What's the loop?

The worsening of conditions triggers a major contraction of population which worsens the conditions further (contemporary economies take contraction badly and at sufficiently low population numbers and densities advanced technology becomes problematic) which triggers further contraction of the population...