For starters, I don't like milk, no matter what the source or type. So this is not going to be a love letter to raw (or low temp non-homogenized) milk. However, I still need milk in my life. I need it to make yogurt, bread, buttermilk, creamy soups and sauces, and to feed to my husband and daughter, who will occasionally partake in a glass (my son is like me- can't stand the stuff. It's one of two things we have in common).
But commercially prepared milk, particularly those that are ultra pasteurized like a certain organic brand I won't name (yes I will, Organic Valley), have been so altered they no longer resemble real milk. First, the milk comes from cows that spend their days inside, fed unnatural diets of corn, soy, and other by-products as well as growth hormones (to increase production) and antibiotics (to treat the mastitis caused by the growth hormones)... in all fairness, Organic Valley at least doesn't partake in that nonsense. The milk is then super heated to kill any possibly harmful micro-organisms (which ironically makes them more susceptible to infectious bacteria, as the beneficial micro-organisms in raw milk help fight off bad bacteria). This heat also destroys all of the temperature sensitive enzymes and vitamins like vitamin A, which is why milk has to be "fortified." As if this weren't enough abuse, the milk is subjected to homogenization, when the milk is forced through progressively smaller screens in order to make the milkfat into smaller particles- a process that is regularly done simply to ensure a uniform product.
Even without research, this is a lot of refinement on what could be a wonderful whole food. Homogenization in particular bothers me because they don't even pretend it is done for our safety, it is done purely for our "convenience" so that the milk doesn't separate. But since moving here to Minnesota (and after months of looking for a nearby source for raw milk...) I have been lucky to find Cedar Summit Farms Milk, which is grass fed low temp pasteurized non-homogenized milk. It comes in beautiful glass bottles, with a little cap of cream at the top. When I use it to make yogurt, the yogurt develops a delicious and lovely layer of cream at the top. It's a little pricier than "regular" milk (but really, not much, and we get a deposit back on the bottle).
But why? I mean besides having problems with all the adulteration? The benefits of raw milk are pretty obvious and pretty easy to back up, so I'm not going to go into that. But I will explain my problem with homogenization. There is a theory that the process that breaks down the fat particles also makes them smooth, which in some way makes them more likely to enter the blood stream, stick to the blood vessel walls, and turn to plaque, contributing to heart disease and stroke. This theory has not been proven and some seem to have disputed it pretty strongly. However, I think that it at least is partly responsible simply because of the timing- milk was widely homogenized beginning in the 30's, right before heart disease rates began to rise. Of course, this is also around the time white flour and refined sugar were becoming more popular, so I think that it was a combination of the three as opposed to any single reason. So whether or not someone can actually prove it (and dairy is big business, so no one is really in a hurry to prove that their sole product is bad for us), I've decided homogenized milk is not something I want to give my family.
Those are my reasons. I encourage you to do your own research on this topic if your interest is piqued.