But it's a privilege for individuals in high income countries. The economic impossibilities are tied to the resource side: water, energy, land-use.
Again, I'm far from anti-meat but I am a food systems researcher and the world cannot extract enough resources to feed ourselves mostly beef - or meat for that matter. Nor could we do it at cost.
Perhaps there is a scenario where a majority of the population is directly involved in agriculture and we spend >50% of our income on beef. But then you have a massive reduction in total GDP because more human capital is pulled away from other sectors.
I wouldn't be so sure: markets find ways to satisfy demand. People made similar statements about photovoltaic panels, but here we are, with solar competitive with coal. I'd prefer to let markets organically allocate scarce inputs to their highest and best use over asserting that this technology or that behavior is unsustainable. If you're right, markets and prices will take care of modulating the demand and there's no need to tell individuals that their habits and preferences are a "privilege".
For the past 1500 years ive made it a point to eat nothing but the rancid dew-pocked suet in unattended suburban bird feeders for breakfast. My lunch is a simple trip back to those very same bird feeders, and --you guessed it buddy-- dinner is a quick helping of that sweet greasy nectar of the caged brick full of seeds and lawn detritus. Most people say they cannot believe their eyes when they see what i look like, or how I managed to stay so physically fit, or where all their suet keeps going to.
I hope to start a blog soon where i will expound upon the brilliance of giving up old fashioned coffee as well in favour of a modern advancement in nutrition i call, contact cement and model epoxy.