The "point" that I'm "selling" is this:
So the only question concerns the veracity of the claim that animal agriculture is the biggest-polluting industry. Even if one conceded that animal agriculture was not THE biggest single contributor to the destruction of the environment, it can't be argued that it's not a major contributor.
In turn, the question stands - why do environmental groups urge consumers to make such a huge range of lifestyle changes (swap your light bulbs, recycle, drive less, buy carbon credits to offset your travel etc), but not eating meat doesn't even enter the narrative?
Following from this - why is it that so many people become so defensive (I'm looking at your post, Nick) when faced with these questions. Is it even possible to call oneself an environmentalist, while being an omnivore?