If we stopped killing animals for meat, humans would starve because there would not be enough food to go around.
Food scarcity is an argument for veganism, not against it. As the world’s population grows and more people are able to afford meat, less food is available overall. This is because we filter protein and energy-rich crops like soy and grain through animals at a substantial loss before eating them. Depending on the numbers you want to trust and the type of animal it comes from, each pound of meat requires four to thirteen pounds of feed to produce. By switching to a plant-based diet, the farms that presently grow that feed are able to grow food for people instead.
In all, roughly 40% of the world's arable land is used for food production, while only a quarter of that food is for human consumption. The rest, a staggering 30% of the world's arable land, is used to produce animal feed and commands a third of the world's fresh water. Worse, the meat resulting from this industrialized animal agriculture is not divided evenly. For instance, Americans eat 270 lbs. of meat a year on average, while Bangladeshis eat 4 lbs. Meanwhile, much of the world gets no food at all or raises livestock feed for export to countries with a high demand for meat, creating an unequal burden of production versus consumption between the poorest and richest people on the planet. This is why even conservative researchers are calling for a global decrease in the consumption of meat, while most are calling for the widespread adoption of a vegetarian or vegan diet in order to create and sustain food security for the world's growing population. Widespread adoption of a plant-based diet would leave the Earth's arable land and fresh water for use in the production of food crops for people and not feed crops for livestock.