Ecological damage and collapses occur well before we'd run out of resources. Just because we can encroach on more and more land, at the expense of the environment, doesn't mean there isn't a problem.
Increasing agricultural productivity nowadays doesn't involve encroaching more land. And the developing nations, where the populations are booming, are still on the lower end of agricultural productivity.
Combine that with the fact that populations appear to top off at a certain level of prosperity, and you'll realize that we'll be just fine.
> Increasing agricultural productivity nowadays doesn't involve encroaching more land.
What are you talking about? 41% of US land is used for livestock production. It's not that efficient, and the perpetual increase in population will just push that higher.
> Combine that with the fact that populations appear to top off at a certain level of prosperity, and you'll realize that we'll be just fine.
We don't all share in that prosperity. Population is still set to grow in the (perpetually) developing world plagued by poverty. The population growth rate in the 1st world is a targeted rate, a matter of policy, which is met by increasing immigration. Fertility rates on the global scale won't drop so long as child mortality and quality of life isn't improve across the board, and consequently the growth rate in the 1st world is also here to stay.
