There are vast areas that are very, very poor for growing anything other than some grasses. These lands will not support growing plant based foods for people. However! They do produce plant based food for cattle. You end up with 0.5-2 acres of this land to feed a cow.
>The vast majority of beef is not grazed on lands incapable of naturally supporting more intensive forms of agriculture.
The vast majority of beef is grazed on lands incapable of supporting at a sustainable price point more value dense forms of agriculture. If those ranchers could sell you boutique sustainable tomatoes they would do so in a heartbeat (or as fast as they can given the fact that it's basically a career switch).
You get crops like soybeans and corn where the land will support that and less value dense crops (like beef and timber) in places it won't. You can grow other products on cattle grazing land but you won't be price competitive with the farmers on better land. The fact that this land is used for beef instead of some other crop is a reflection of how efficiently we use the better land. As vegetable product fillers make their way into lower and lower end beef products (as price, technology and consumer preference allows) the land used to farm beef will likely shrink from the least viable areas (the areas least suited for beef) with demand and/or be pushed out of the most viable areas (the areas most easily suited to other crops) by more value dense plant crops. Obviously there's some serious switching friction otherwise you'd see this play out with every little change in commodities prices.
Sure, everybody reducing their meat consumption to their share of what is produced on marginal land would be the optimum, even better than everybody going 100% meatless. How much of the typical meat consumption of a current-day nonvegetarian would that be? 5% perhaps?
And it wouldn't be the same 5% that we see with "almost vegans" today who argue "less but better" to only eat premium cuts while proudly announcing that they avoid all grinder meat. If you want to eat the steak, don't scoff at the sausage.
Back to grazing marginal lands, yeah, I'd also hate to see the animal species that have accompanied us throughout human history go extinct. But we're very far from that.
