Why not? It would be effective. (Need to do something in India as well, of course.)

Additionally, cows are a relatively inefficient converter of plant calories into meat, so other environmental problems can be ameliorated by encouraging a reduction of cow meat consumption to what is naturally supported by the environment (e.g. pastured cows; cows grazing on marginal lands that can't really be utilized for anything else; etc.).

So when the climate effect is positive, and the ancillary effects are positive, what is the rationale to not do it?

(I agree that penalizing farmers is a bad idea--it just shifts the production to places with even poorer controls, which can be compensated for via tariffs and other means, but it's overall sloppy and wasteful.)