Most of our meat is produced in factory farms. Well more than 90% (closer to 99%). The idea of Ol' MacDonald with chickens and cows roaming yards and fields is a long-since dead myth.
Nope. Legumes provide a full spread of amino acids. Those who preach otherwise are either misled, or trying to mislead.
This link has multiple attached articles, discussing how a vegan and/or whole foods plant-based diet (WFPBD) gives you plenty of protein, all the kinds you need, and healthier for you than meat.
The Protein-Combining Myth | NutritionFacts.org
The site itself (Nutrition Facts . org) is a great overall site for questions about the current state of food research (free from big Ag influence).
Even vitamin B12 is actually not a meat item, it is a soil material (i.e. - it was in the meat we ate, because of feces from the slaughtered intestines spilling onto/into what you ate - that gave us B12). With some modern very sterile butchery techniques, the meat is now deficient in B12. The answer for plant-eaters (and for clean meat eaters) is to take a daily B12 vitamin......or go outside and eat a daily spoonful of topsoil.
As for the OP. As mentioned, we have no need to harvest animals like we did in the past. So why do it? Once you get used to WFPBD, even those tasty-tasty burgers will make you drastically ill, real fast!
Plus, and more important than emotions or morality, is that Veganism/WFPBD uses MUCH less land area (clear-cutting forests) and MUCH less water than raising meat. Much better for Global Warming: Eating this way is actually better than switching to an electric car, or getting solar panels for your house.