Well, diminishing food supply not right now, but generations in the future, when population growth has continued to grow exponentially.
Of course, maybe I don't have a right to talk about this, because we're certainly not "putting (all) our money where our mouth is" right now -- though we do prefer (but can't always afford) to shop in our local farmers' market, and my dh is working on revitalizing the dirt in our yard with earthworms, and trying to figure out ways to get a bigger yield of vegetables each year, without doing anything harmful to the environment.
But if our nation's government made the shift to more sustainable practices -- well, it would certainly help us to make the shift, too. When cash is limited, and you know you can shop Aldi's, or even Price Chopper, for a fraction of the cost at the local health food store ... well, frankly, it's just so tempting to buy the larger quantities of food at cheaper prices, and have some money left over for the other things, and experiences, our kids want to enjoy.
What gets me is, I've heard that there are all kinds of government subsidies for big agriculture -- so surely those same subsidies invested in sustainable, organic food-growing, could help to make organic foods more affordable to the general public. So food production would gradually level off, and population would gradually level off in response. And at the same time, we'd all be supporting the shift to a more livable way of life.
Quinn makes an interesting point, that the advent of contraception really hasn't resulted in a reduction of population world-wide. He thinks (or maybe it's just my interpretation of what he thinks) that if governments would quit subsidizing an ever-increasing food supply, that would do more for population concerns than contraception. And he's not talking about producing too little food, and forcing some people to starve to death: he's saying we should produce enough, and quit aiming for an excess.
Because the excess isn't accidental: it's actually planned and aimed for each year.