The problem is the concept of externalities, which means that capitalism will happily overshoot our sustainable resource base, and then collapse. It's the Minsky Moment at ecological scales.

An ecosystem contains many species at equilibrium, but the ecosystem itself consumes all available resources.

But that equilibrium can be maintained by those resources being replenished within the ecosystem through the actions of components of that ecosystem.

In our example, that's not happening. The resources are being exploited and not replaced.