The emissions related to those calories would go away.
If we have a magic wand and that disappeared entirely tomorrow, that would simply be allocated to other areas. There’s a reason sodas in the US are sweetened with HFCS and our gasoline is cut with ethanol produced from corn - because of lobbying efforts to subsidize corn production, which has driven down costs, which in turn made it profitable to use corn in ways where it wouldn’t otherwise make sense. Europe uses ethanol derived from sugar beets, which is significantly more efficient in terms of CO2.
It’s significantly more complex than “if we reduce beef consumption, we’ll reduce corn consumption”.
I guess I didn't try to spell the whole thought out, but I wasn't trying to claim that beef consumption is an island, I was thinking about how CAFO style animal husbandry supports a lot more animals than pure grazing would.
Assuming we stopped cow farming completely and the fields were turned into wild live reserves of bison or something would emissions magically go down? Or do they no longer count as anthropogenic so we can magically ignore them?