The argument for omnivorianism that I find unassailable is that plowing which is required for annuals is actually worse for the environment than ruminant emissions. While utilizing perenials will require ruminants for a truly holistic agriculture that cycles all nutrients efficiently. So a Perennial plant base agriculture with ruminants to hlelp cycle nutrients is the best ag option available, so eating a few a of the ruminants as they age out of the cohort makes sense, and would be wasteful not to do so.