Earlier quoted context omitted.
Methane emissions and ethical reasons (if you care about such things). Edit: also they take a lot of land to feed. Soy grown in where Amazon rainforest used to be and so on.
If you eat meet which has been raised on ground where trees have been felled for the sole purpose of creating that meat then yes the amount of carbon released is going to be insane. Here in the UK (nearly?) all the meat we consume is grown nationally, i.e. doesn't originate from places like the Amazon. And on the methane front, they eat the carbon in the grass which has literally just captured a bit of carbon from th…
It actually doesn't matter if you grow the feed nationally or import from Amazon, the fact remains that those fields replace a natural ecosystem that could be contributing to biodiversity and much more efficient carbon capture.
Grass captures CO2 from the air, and the cows fart (actually mostly burp) out methane that is about 25 times worse GHG over a 100 year period.
You want to get better at working with nature? Hunt your own meat from the wilderness.