The environmental issue with raising livestock isn't that they fart. It's that they convert energy from plants to energy stored in their flesh with low efficiency, so to raise livestock, humans need to grow more plants — and use more resources — to feed the livestock than they would need to grow if the humans ate the plants directly.
I find that people concerned with animals rights tend to emphasize ethical arguments over (valid) environmental arguments, while those emphasizing the environmental arguments are genuinely concerned with the environmental cost of animal agriculture. In other words, most people making environmental arguments against animal agriculture are not trying to trick you.
There's more to it than just energy. As a practical matter, nutrient quality is tremendously important. Some animals, particularly ruminants (cows), are able to convert low-quality plant matter into high-quality easily digestible protein with amino acid ratios that closely match what humans need. It's the bacteria in their guts that perform the conversion. We can certainly get what we need from plant sources but this requires careful meal planning to obtain the right amounts of essential amino acids without exceeding energy balance.
You are clearly discussing this in good faith, thank you.
> In other words, most people making environmental arguments against animal agriculture are not trying to trick you.
Sadly ven diagram of animal rights advocates, clueless do gooders and environmentalists overlaps greatly.
Bad faith arguments emerge not only by extremists but also by people eager to be part of the movement with no capacity for independent thought. These things take root and become "common knowledge" within the communities.
They don't need to be actively trying to trick me to muddy the waters with their own, however well intentioned, confusion.
We are still dealing with metaphysical arguments - note you didn't provide any numbers or scale or externalities or consideration towards second order effects or unintended consequences.
I can give a contrived example in the other direction (as its easier to recognize the obvious flaws):
Cars bad. Bicycles good. Clearly. Bike lane therefore must be good. Now you get a dozen guys in spandex burning extra calories and compensating by consuming far more burgers than they otherwise would have. And far worse traffic idling their engines at less efficent stop-and-go low speeds for longer.
What was actually accomplished in terms of CO2? We should ban all bicycles instead.
