I assume they're referring to the inability of small scale agriculture to produce as many calories per acre as our current food system, which also relies heavily on fossil-fuel based imports. Of course, we also have a lot of unnecessary (but tasty!) excess in our current food system too.

I think the problem really becomes - what do you do when the current system becomes untenable? If the costs of a "basic" modern life (housing, transport, food - I'm not even including healthcare here) become impossible for someone on the median income to have, then what, exactly, are they supposed to do? Find a nice corner to die in?

We sorta tried a miniature version of this on a few acres in Ireland and while it was tough (and we were always reliant on the outside world, we didn't literally homestead), I'm not sure it wouldn't be an improvement for a non-trivial percentage of people at the bottom levels of society.

But, of course, land is owned (thanks to enclosure, which took a common asset and allocated it to specific individuals), and this all falls apart when you or a loved one have a serious disability or illness.