We have only been at it for so long, and barely gotten started in earnest. Plus... energy and additives are not "external" to the system: they are provided by a natural species in the system, us.
Yes, we do need to get to a point where we are not relying on expendable reserves to run the system. But it certainly is possible that we will engineer a better ecosystem (robot cultivators and solar panels included) that results in a more efficient net benefit for us.
Yes, we do need to get to a point where we are not relying on expendable reserves to run the system. But it certainly is possible that we will engineer a better ecosystem (robot cultivators and solar panels included) that results in a more efficient net benefit for us.