Altered behaviour would trigger market forces. We cannot predict that 'there wouldn't be enough food' when we're currently wasting calories and fuel growing meat.
That's what I figured but I wanted to make sure. Although it seems to me humans wouldn't let all the land grow wild again. It is more likely that we would re-purpose it to some other human based activity. Humans tend to view previously occupied lands and wilderness as either "waste" or "potential".
I tend to see it as 'a natural resource to use (even consume) wisely'.
But I want to point out that there are many dimensions to the issue with factory farming, and they're independent of each other. We have a hard time with adding factors when it comes to morality. Two independent reasons should add to each other, but people who are experience dissonance will
combine the reasons why it doesn't apply to their case.
We're experiencing a huge extinction event, and part of that is
conversion of land-use. Factory farming contributes because we need a lot of grain to grow a cow, and so we increasingly convert land that could stand as a buffer system in extinctions. Slowing (or even reversing) this trend would slow the current anthropomorphic extinction rate.
Extinctions are like bankruptcies in an economy. A low-boil of bankruptcies is expect, or even fine. A higher rate might be tolerable. But there's a tipping point where things just get worse.
A second factor is that we use an incredible amount of
fossil carbon in order to grow meat. Look at a liter of diesel. By some approximations, that's the amount of fuel used to provide you with one day's food. That's a lot, and it's (obviously) unsustainable. More importantly, it's one of the greatest drivers of climate change (which also has a series of independent reasons to be slowed).
Factory farming animals is one-two hit on our ecology and on our environment.
I'm just one person, my shopping habits aren't going to change anything, though. If I saw tens/hundreds of millions of people doing this, then yeah, that'd be something I could get behind and alter my lifestyle for. But that isn't happening.
I know. You're loathe to modify your behaviour regarding environmental issues until you find you are following everyone else first. Or you're forced by legislation.