Doesn’t even need to be green, just any sort of plant or really any sort of organic matter. Eating goats that have lived off of old trash is probably not the best idea though

Which neatly raises the point of how modern large monoculture does a lot less of that kind of use of agricultural products unusuable by humans.

Absolutelly, the whole of a cow slaughtered in a slaughterhouse is famously used (down to the hoves) and nothing thrown out, however you don't see goats being raised on the unusable parts of a corn plant (whilst wheat straw is actually used as feed, for corn the silage for cattle made from it uses the whole plant including kernels not just the left-over unusable by humans parts).

The industrial farming of corn in the US requires using hybrid corn strains to reach the yields it has, which in turn requires the use of fertilizers because the natural soils is incapable of sustaining the density of corn plants that hybrid varieties achive.

Those fertilizers in turn are mainly made from Oil, which is a non-renewable resource, making the whole thing unsustainable. It's is possible to make the fertilizers sustainably, it's just much more expensive so that's not done.

The US is so deeply involved (including outright military invasions) in the Middle East from where most of the oil comes because in the US oil it's not just a critical resource for Transportation and Energy, it's also a critical resource for Food because it's so incredibly dependent on corn (which is estimated to add up directly and indirectly to more than 70% of the human food chain there)

PS: There is a book called The Omnivore’s Dilemma which is a great read on this.

"Modern farming techniques consider sustainability"

Yeah sure. They consider sustainability in that the current generation of poisons they use haven't been proven unsustainable YET. When they are proven unsustainable, they'll move to the next generation, that hasn't been proven YET...

Also systemically annihilating everything except that one crop you want to grow makes your farmland an ecological desert, that doesn't sound very sustainable either.

Unless you're of the conviction that farmland shouldn't be in any way part of nature, and we should concentrate on just growing crops there and every other kind of life there should be discouraged, and by doing that as dense as possible we keep more space for actual nature.

Though i think farming that leaves meaningful room for (some) nature to coexist with it doesn't do that much worse in yield to make the modern 'kill everything' approach worth it. But we'll see what the future brings i guess.

But just being like 'modern farming techniques consider sustainability' seems pretty naive to me...

Modern agriculture uses ammonia pellets that more than half will evaporate by the time it enters the soil and it seeps into aquifers and rivers.

There is nothing sustainable with modern agriculture.