As infant's we are only sustained on milk...
Milk is an exellent source of Calcium, necessary for bone growth.
Apparently, our ancestors thought, "hey, if we drink milk as babies, why don't we do it now?" Goat milk is also ok for human consumption, but I think most people would prefer Cow milk.
I wouldn't call "Milk does the body good" garbage.
Milk provides:
Vitamins D and K are essential for bone health.
Iodine is a mineral essential for thyroid function.
Vitamin B12 and riboflavin are necessary for cardiovascular health and energy production, and B12 is difficult to get outside of animal products or else as supplemental pills.
Biotin and pantothenic acid are B vitamins important for energy production.
Vitamin A is critical for immune function.
Potassium and magnesium are for cardiovascular health.
Selenium is a cancer-preventive trace mineral.
Thiamine is a B-vitamin important for cognitive function, especially memory
Conjugated linoleic acid is a beneficial fatty acid that inhibits several types of cancer in mice, it has been shown to kill human skin cancer and other cancer cells in vitro studies, and may help lower cholesterol and prevent atherosclerosis; only available in milk from grass-fed cows.
Studies show possible links between low-fat milk consumption and reduced risk of arterial hypertension, coronary heart disease, and obesity. Overweight individuals who drink milk may benefit from decreased risk of insulin resistance and type 2 diabetes.