Pasteurization kills all the enzymes that help your body break down milk.
Without pasteurization, milk is a perfect food. When pasteurized, it is a dead food that causes lots of problems. Lactose intolerance became a common thing after pasteurization and enough time passed that people never had real milk in their guts.
Homogenization seals off all of the good milk fats into tiny bubbles that your body cannot easily get at, so they mostly pass through your body without any of its wonderful nutrition getting to your body.
Milk is actually very safe. The body has defenses from diseases, and the mammaries have even more defenses to make sure no bad things get passed to the child. So, the cow has to be very sick for you to get sick from milk. However, when you have a ton of cows in a small area (as many industrial farms) and you feed them a bad diet (like corn and antibiotics) and you don't personally go out and look to the health of each cow, well then, just pasteurize it to make sure nothing living gets through.
Healthy animal = healthy milk!
Unless they get into the sour grass. Then it is sour healthy milk. ^_^
I used to tell my kids to look for brown cows 'cause that's where chocolate milk comes from. Just passing down the crap my parents told me. LOL
My dog can tolerate small amounts of raw milk.