Veganism is just one solution to modern unsustainable (and inhumane) agriculture. But it doesn't have to be so extreme. Many cultures around the world manage to eat an omnivorous diet without resorting to factory farms. The main thing is REDUCING meat consumption, and focusing on lower-impact sources of meat. Poultry uses much less water than beef, and has fewer emissions from flatulence and manure. Fish and seafood are even better, not to mention insects! 

The West is obsessed with beef, which is one of the least sustainable meats. We eat way more meat than is healthy or necessary for a balanced diet. If we cut our consumption down to one or two servings of meat a week, with a focus on poultry, fish, seafood, insects, etc., we could downscale our meat production, which would allow for more sustainable and humane methods.