Wild animal grazing where we're not killing them and breeding more every year has tremendous environmental benefits. Killing them and eating them is not compatible with the environmental benefits of grazing:
>Small numbers of grazers may be consistent with healthy ecosystems and have minimal greenhouse gas impact, but only if their populations stay within ecologically defined limits.
The number of grazers that are needed to maintain a prairie or plains ecosystem is far higher than most people assume, and vast spaces in the US are becoming forested because of lack of wildlands management.
OK, we need a lot of grazers. That still doesn't really help with the fact that 30 million bovines are killed and "restocked" on a yearly basis. If the argument is "we can keep eating meat at the current rate because we need a lot of grazers", I don't think it's a very good one. Whatever carbon sequestering benefits we were supposed to get are almost immediately invalidated. It's the same issue with trees - you don't realize the carbon sequestering benefits of planting trees until they've been alive along enough to offset the input carbon.
Taking as a given that we've eliminated 99% of natural predators, there's nothing inherently ecologically wrong with humans eating cattle instead of wolves eating bison.
I believe the distinction here is scale. The rate at which natural predators killed bison is only a small fraction of the rate that cattle are killed for food.
If human livestock consumption were closely matched to natural grazer consumption, essentially acting as a 1:1 replacement, this argument makes more sense. I don’t think that’s been true for at least a century at this point though.
Citation needed. A quick Google search says the US has about 90 million heads of cattle, while the peak population of wild bison was 60 million and of wild deer was 40 million. That seems pretty close.
