Meat is actually more natural for us to eat than dairy, eggs, and other harvested animal products. We were hunter gatherers before we were sedentary agriculturalists. Humans have had a longer history of gathering plant matter and occasionally hunting for meat than they have of cultivating honey in bees, milk in cows, and eggs in chickens. The Skinny Bitch authors target dairy specifically for being unnatural:
"When we have babies, we breastfeed them, and then at a certain point, we stop. We don’t breastfeed our grown children, or our husbands or friends, for that matter. It is exactly the same for cows and every other mammal on the planet. They produce milk when they give birth, they feed their young, and then they stop. We are the only species on the planet that drinks the milk of another species. We are the only species on the planet that drinks milk as adults. Why? Because the multi-million dollar dairy industry has convinced us that we need milk for healthy bones. That without cows’ milk, we will shrivel up or shatter. However, Yale researchers found that countries with the highest dairy and meat intakes also suffer the highest osteoporosis rates.
The truth is, we can get adequate calcium from leafy greens, vegetables, raw nuts and seeds, and beans."
I would argue much the same for other animal products. While there are some species that eat the eggs of other animals, human can't eat them without cooking them first like these other species can, and we can't get many other animal products, like wool and honey, without farming, which, again, is a more recent phenomenon than hunter gatherer lifestyles.
Once you point out that, in fact, all animal products except maybe meat are nonsensical (I mean, meat is nonsensical since we can't eat that raw either and what other species has to cook its food?? it clearly demonstrates our bodies weren't equipped to eat meat. but just for the sake of winning the argument...), you could mention something about "maybe there should be a diet that is vegan plus meat"? But then you can discuss that even if humans historically have eaten meat and are meant to eat meat (which I guess some might consider debatable), meat ruins the environment so badly that there is no ethical justification for it (since some people might also be able to argue against the ethics of eating meat, but the environmental damage is a cold hard fact).
Anyways, I was just brainstorming about attacking dairy and eggs before going in for the
