I'll share what I just hammered out for them.
Eating meat is like slavery, or sexism, or three-martini lunches. It’s something that’s ethical and accepted as long as a preponderance of the citizenry believes it is. Cow eating isn’t accepted in Hindu countries. Three-martini lunches are not sanctioned in Muslim countries. For me the key question isn’t whether it is ethical, but what will the arguments that make it unethical be?
Will it be health? Of course too much meat isn’t so good for you, but then again too many three-martini lunches aren’t either (how did big-business make it through those Mad Men days?). It’s quite possible to live a healthy and satisfied life eating no or very little meat. Probably will make you live longer too. Of course, we all know (or think we know) what’s good for us food-wise and that hasn’t stopped our obesity crisis. Eating smaller portions and exercising can accomplish the same goals.
Will it be animal welfare? Welfare is a tricky issue. Greater awareness has led us to think more about how our animals are raised. Indeed, the fatty-acids in pasture-raised beef are healthier than those in feed-lot raised or ‘finished’ beef. Thus, free-range beef is a good thing for the animals and for us. But then again, you don’t have to eat beef to eat meat. What about chickens that are sold as free range but are afraid to venture out of their large indoor yards? All of these raised animals must be killed. Is killing something to eat it, just because you want to, ethical? Well, we did evolve as omnivores. But then again, we also evolved with large creative brains that can create Ponzi schemes, extortion rings, and design genocidal campaigns. As the Naturalist Fallacy says, just because it is, doesn’t mean it ought to be. But I think many arguments against meat eating fall away when you’re eating small amounts of humanely raised and humanely slaughtered animals.
Is it ethical to eat fish? Probably not most wild fish. Not only are they caught in entirely inhumane ways--would you like to drown on a line, be scooped from your home surrounded by screaming neighbors, or be hooked, pulled outside and then left to die on ice? But, by eating fish, you’re also creating a huge ecological crisis—we’re eating our way down the food chains in the ocean. Think you can solve the wild-caught fish problem by growing them? Aquaculture creates large-scale marine and estuarine pollution. And, when you’re growing carnivorous fish, you’re catching wild fish to feed your captive fish. Now that doesn't make much sense. However, fish eating will be self-limiting as we fish down the seas (got any good jellyfish recipes to share?) and as fish-eaters poison themselves with mercury and other toxins. As long as it remains ethical to poison yourself, it’s ethical to eat fish.
Will it be climate change? Livestock production produces a healthy percentage of methane—a potent greenhouse gas. Eat meat and melt the artic ice cap! It’s funny to think what we take for granted now and view as acceptable will someday be viewed as selfish and thoughtless. Slavery used to be OK. Will car driving or meat eating fall into this category of ‘once were acceptable’? If, however, you’re concerned about climate change, eat less meat.
What about engineered meat? Is it ethical to eat a cell culture that involved no suffering? PETA seems to think so because they, and other welfare organizations, are supporting research into ways to mass produce engineered meat. But why would you want to? Wild fish and animals taste so much better.