It doesn't matter how they're grown / bred. You still have to feed them, which means cutting down vast areas of rainforest to grow grain. And they'll still produce billlions of tonnes of shit, which emits the vast majority of methane gases which is the single greatest contributor to global warming.
It is pretty easy to seek out examples of cattle not reliant on rainforest grain. You just need to live somewhere with reliable rainfall and abundant grass.
As a carnivore what if I live off local rabbit ? What is the impact on the environment ? Just for arguments sake, what if I only eat rabbits, shot by farmers to stop them eating their lettuce and other precious herbivorous crops ?