There appears to be no health requirement that requires us to eat anything from animals, meat, eggs, or dairy. Elephants, and horses develop massive bodies and strength from diets only including plants. And for humans, Dave Scott was vegan and won the Ironman Triatholon 5 times (swim 2.4 miles, bike 112 miles, run 26.2 miles), and Carl Lewis's athletic perfomance when he was vegan.
Even the mainstream governmental health agencies conclude that fully-plant diets can be fully healthy for humans...
The American Dietetic Association says:
"Well-planned vegan, lacto-vegetarian, and lacto-ovo- vegetarian diets are appropriate for all stages of the life cycle, including pregnancy and lactation. Appropriately planned vegan, lacto-vegetarian, and lacto-ovo-vegetarian diets satisfy nutrient needs of infants, children, and adolescents and promote normal growth (36,114,115)." http://www.eatright.org/Public/GovernmentAffairs/92_17084.cfm
And also, animals used for food do not live in pastures like they used to. The unneccessary animal foods involve abuse to the animals. Family farms are fewer, and factory farms are the majority. Now, most of the animals are artificially inseminated, taken from their mothers within weeks or days, caged or housed in crowded warehouses, and then killed... 10 billion+ in the USA a year according to the USDA.
As for eggs, the majority come from hens who are forced to spend their lives in cages, with less floorspace than an 8.5" x 11" piece of paper. They have their beaks clipped so they won't peck at the other hens in their crowded cages, and they are forced to go through periods of being starved from food and water in order to increase egg production (forced molting). Their feet stand on thin wire mesh constantly so their wastes can drop through.
All of these harms are clearly true since McDonalds even mentions them publically. Thanks to people who spoke up, McDonalds improved their guidelines for egg producers to follow... people can help changes happen through how we spend. http://www.mcdonalds.com/usa/good/products/hen.html
(note that 72 square inches of space for each hen for their entire lives is about 80% the space of a piece of paper :(
"The board recommended that the United Egg Producers either discontinue labeling eggs as “animal care certified,” or significantly alter it to stop misleading consumers."
“It is unimaginable that consumers would consider treatment they find ’unacceptable’ to be humane treatment,” the ruling stated.
"While the BBB found that the egg industry’s standards have improved treatment of hens, it’s not to a level that most consumers would find humane."
And dairy too... Cows are killed after about 5 years of a normal 15 year life. Also cows only produce milk just like humans, when the mother is pregnant and shortly afterwards. They are forced into pregnancy and the calves who are born either end up as veal calves, are killed for chip beef, or become future dairy cows. Veal calves have no bedding, are kept in small stalls, are tethered at the neck to restrict them from moving in order to keep their muscle(meat) more tender, and are fed a liquid diet in order to keep their muscles tender.
...life is very real and important for all animals, just like life is real and important to us