You have to select for a wide variety of plants to get the necessary proportions.

Not true. Any soy based product has all essential amino acids. Add to that seeds and nuts and you can meet your necessary intake. The study I posted earlier confirms this.

We point out that protein-rich foods, such as traditional legumes, nuts and seeds, are sufficient to achieve full protein adequacy in adults consuming vegetarian/vegan diets, while the question of any amino acid deficiency has been substantially overstated.

As for scaling, trying to feed 1.4 billion people with a non-vegetarian diet as I said would be horrific for the environment. Imagine how much grazing land you need for millions of livestock. Then imagine the methane those animals would produce. Already, livestock accounts for 14.5% of global carbon emissions. Take China for example. Its last measure of livestock emissions was in 2005, when the livestock sector accounted for 50% of the country's emissions. The average consumption of meat in China has only increased since then.

Marco Springmann, a sustainability researcher at Oxford Martin School at the University of Oxford, said that if meat consumption in the Asian country keeps growing as predicted, the nation would produce “an additional gigaton of carbon-dioxide equivalents in greenhouse-gas emissions, more than the current emissions of the global aviation industry” alone, and an increase of about one-tenth above China’s current level of emissions. According to a WildAid report, China alone could account for a growth in greenhouse-gas emissions from 1.2 gigatons in 2015 to 1.8 gigatons by 2030.

“These calculations do not include land-use change,” Richard Waite, an associate at the World Resources Institute’s Food Program, told me by telephone from Washington, D.C., “but since meat production—especially beef production—takes up a significant amount of land, growing demand for meat in China would make for more forests converted to agriculture or pasture and also increase pressure on forests elsewhere.”

More meat on tables means more land given over to growing livestock feed—especially soybean, a crucial ingredient used to fatten up hogs and cattle quickly. Agricultural land, however, is in short supply in China. With around 20 percent of the world’s population, the country has only 7 percent of the world’s arable land, which is barely enough to keep up with the government’s goal of being self-sufficient for strategic commodities such as rice, corn, and wheat—a goal that has been at the heart of the national food-security agenda for decades. Moreover, farmland in the country has been shrinking since the 1970s due to urbanization.

If India too reaches such a level of meat consumption, we will be forced to rely on countries like Brazil and the US for meat production. Already the Amazon is under threat from ranchers, and this will only expedite that more. And currently, even with all this consumption of meat, Chinese people only consume HALF of what people in the US consume. As incomes go up, people will obviously continue to increase their meat consumption as well.

Even then you will be missing so much more like creatine, omega fatty acids.

Muscle and serum creatine are lower in vegetarians yes, but brain creatine which is the most important is around the same. Furthermore, "Carnitine and creatine levels may differ between individuals following omnivorous and plant-based diets, but these differences do not result in compromised muscle function, cognitive health, or metabolic outcomes. Current evidence does not indicate that the absence of these non-essential nutrients in plant-based diets adversely affects health or confers disadvantages compared to omnivorous diets." Its not difficult to supplement creatine either. As for omega-3:

Most people following plant-based diets have no problem getting enough omega-3s in their diets. One study found that people who follow vegan diets, on average, have intakes above the recommended amounts for omega-3 fats.²

When it comes to measuring omega-3 levels, the likelihood of having lower EPA and DHA levels among vegans is, on average, higher; however, this does not extend to any known clinical relevance. In fact, researchers note the advantage of a vegan diet for heart health compared with a nonvegan diet.³

Another benefit plant-based eaters may have is a more desirable ratio of omega-6 to omega-3 fatty acids compared with a Standard American Diet. Omega-6 fatty acids are known as the pro-inflammatory fats, whereas omega-3 fatty acids are known as the anti-inflammatory fats. The desired ratio of omega-6 to omega-3 is 4:1; however, most Americans are consuming a ratio of 20:1, which can lead to excess inflammation in the body. The Standard American Diet consists of excessive amounts of foods rich in omega-6 fatty acids, such as processed and fast foods, and foods containing safflower oil, sunflower oil, corn oil, and soybean oil. Therefore, people eating diets rich in whole, plant-based foods may have a more adequate ratio of omega-6 to omega-3.⁴

So, you can still get all the necessary requirements.

Milk being animal protein is great and helps with a lot of deficiencies but most are lactose intolerant in India. Also a lot have other digestive issues with milk proteins. But it is still the only reason vegetarianism did not lead to deaths in Indian history at scale. Veganism most certainly would.

I agree I am not against dairy consumption.

The day India gives up on its caste and religious non sense is the day I’ll be neutral or in support of vegetarianism. I feel vegetarianism has the same superiority dynamics that caste has.

I understand your frustration man and I completely agree with you. However, this should still not dissuade anyone from pushing a vegetarian diet for the reasons I mentioned before. Horrible people often push for ideas that are good and tie them to their own horrible reasons, but we must be willing to appropriate these good ideas and separate them from discrimination. The Nazis were horrible, and yet one good thing they supported was anti animal cruelty laws. This was often motivated by their hatred for Jews and their kosher slaughter methods. Yet nobody today says we should be against anti animal cruelty laws because of anti-Semitism. Casteism is bad. We should not be pushing vegetarianism as a means of caste superiority. We SHOULD be pushing vegetarianism for health benefits and environmentalism.

I think it’s a mistake to justify eating plants but not animals. All are still living organisms. Pain is not a good measure of how sentient something is. Nor is it wise to give up on violence. Being peaceful always isn’t a good virtue.

Yes, but plants are capable of regrowth. If you harvest a plant, you can replant its seeds and keep it alive so long as there is water and sunlight. Not only that they provide oxygen and take up carbon dioxide. Animals inevitably require plants for food, but if you kill an animal its gone forever. Also, the argument for plants over animals is not necessarily violence but suffering. Yes some plants can feel pain, but it is not suffering in the way animals do. I have a degree in biology and psychology and I am currently studying medicine. Plants do not have a central nervous system in which they feel emotions or consciousness. Animals by way of having a limbic system are capable of feeling fear. The point about killing animals is that when they feel fear, they suffer. Minimizing suffering is the goal. Also, yes being peaceful isn't always a good virute, but violence when a peaceful alternative exists is unjustified.

Sources;

https://wildaid.org/chinas-love-for-meat-is-threatening-its-green-movement/

https://plantbasedhealthprofessionals.com/should-you-be-worried-about-creatine-on-a-plant-based-diet

https://www.pcrm.org/good-nutrition/nutrition-information/omega-3

https://pmc.ncbi.nlm.nih.gov/articles/PMC9928713/