It's apparent that most people using this argument to promote vegitarinaism know nothing about farming. Vegetable crops require a lot of what farmers call "inputs". These are things like water, highly fertile land, fertilizer, labor intensive cultivation, and labor intensive harvesting. These things make growing vegetable crops expensive. The biggest problem is land. The amount of land that is suitable for growing such crops without very high inputs is relatively small.
I have to admit, I have never before heard the argument that growing vegetables is a bad idea because it's expensive. You would think that with 10,000 years of agriculture under our belts that we would know a couple things about issues like crop rotation, cultivation, and harvesting. Apparently we aren't very good at agriculture though, I was not aware of that. I just sort of assumed that since there are farmers in every single country, and since there has been agriculture going on for the last 10,000 years, and since there are a ton of unskilled workers looking for jobs, and since we can produce fertilizer to replenish land that is not rotated, that maybe we would be able to grow some crops by now. Maybe that's something that science can get on and figure out.
Please don't persist with that argument, that is a disingenuous argument. Here's a farm in America that has been operating for over 370 years, somehow they have managed to not destroy the land. It's almost as if farmers understand how plants interact with their land, and how they are best able to use the land. As for the shortage of land, I live in a desert. Most of our land is sandy dirt. The soil in my backyard garden is pretty awful, it requires help to support most crops. But that doesn't stop people from farming here. Look at this satellite image. You see all of those green areas to the west and south of the city? Guess what those are. This is nothing new, either. Before any white people settled this area, the Hohokam tribe was here. Guess what is one of things that the Hohokam people are known for. I'll give you a hint: Phoenix has canals going all through it that are not exactly modern.
We cannot sustainably and affordably feed the world without animal protein .
That is simply not true. Replacing huge animal farms with vegetable farms is a real possibility. If you want to talk about wrecking the land, stop by a stockyard with 10,000 head of cattle and see how that land is doing.
The fact still stands - right now, today, we are currently producing enough grain to feed the entire world. We don't even have to change anything! It's happening now! The only reason we aren't feeding the entire world with that grain and those crops is because we are feeding them to livestock, which take a lot of grain and produce a small amount of meat for a small amount of people. Americans use 220 pounds of grain per year to eat, and 1500 pounds per year to feed livestock. It does not take a doctorate degree to realize that those 1500 pounds of grain can go to people instead of livestock, and can be used to feed more people than the livestock can.
You want to talk about "inputs"? Let's talk about what is required to grow a cow from a baby to an adult 1,000 pound steer. Cows will consume between 1% and 4% of their body weight daily in food. For a 1,000 pound cow, that's 10 to 40 pounds of food per day, enough for several people. A cow will drink between 40 and 80 liters of water per day depending on temperatures. That's enough water for around 20 people in a day. They also have to be monitored for disease, because you wouldn't want something like Mad Cow spreading through a huge herd in a matter of hours or days and killing all of the cows that you have poured so much food and water into. They also need a low-stress environment, shelter, veterinary care, and a host of other things that do not apply to plants. And once that 1,000 pound steer is slaughtered, you end up with a 615 pound carcass. Once dried and butchered, the carcass would produce around 430 pounds of beef. So you end up with enough beef to feed between 300 and 400 people for a single day. In order to get that beef for those few hundred people to eat in a day, you had to feed a cow several thousand pounds of food and several thousand liters of water over a period of several years, while providing care and handing for the thing the entire time. And if one of them dies of disease? Everything is wasted.
So please, you'll excuse me if I think that your argument about "inputs" for vegetable crops, which can be produced and harvested every single year, year after year, is a little bit disingenuous.
Don't take my word for it, though. Feel free to research the diets of the poorest countries, and see how they all subsist of a diet of pure meat, with no vegetables because vegetables are just too expensive. That's how it should be, right? Maybe start here. Look at the diets of Africans, or people in developing Asia, or Latin America, and tell me how their diets relate to the US and Europe with regard to the percentage of meat versus other sources like cereals.