Answer:
Some arguments may include:
-farmers in the developing countries could would suffer since arid and semi-arid rangeland can only be used to raise animals, (like the Sahel land strip in Africa next to the Sahara). Nomadic groups that keep livestock there would be forced to settle permanently and lose their cultural identities if there was no more meat
-Everybody currently engaged in the livestock industry would need to be retrained for a new career (agriculture, reforestation or producing bioenergy). Failing to provide career alternatives could lead to mass unemployment and social upheaval, particularly in traditionally rural communities where career opportunities aren’t as easily come by
-Taking livestock away could have a negative impact on biodiversity, as their grazing has shaped the land for centuries. Some farmers could be paid to keep animals for environmental purposes.
-Many communities around the world offer gifts of livestock at weddings and celebrations. (For Ben Phalan at the University of Cambridge, this is “why efforts to reduce meat consumption have often faltered”.) Meat used in traditions and holidays would meat losing heritage
-There would need to be a replacement for meat with nutritional substitutes. For the world’s estimated two billion-plus undernourished people, meat and animal products are a must (it contain more nutrients per calorie than staples like grains and rice)
-One World Wildlife Fund (WWF) study found that vegetarian protein alternatives, such as tofu, produce more greenhouse emissions than raising livestock
-Often, raising livestock is the most efficient method for producing food. Most (around 90%) of the land in the US is unfit for most natural crops (most are now GMO). Livestock are not picky when it comes to agricultural nuances that effect crops
There are surprisingly a lot of solid arguments against reducing meat consumption, more than I can list. Check out this site in particular for more specific evidence: https://vegetarian.procon.org/
