"Not identical but similar and arguably better from some nutritional points of view.
Cow's milk? Well, most mammals lose the ability to truly digest it before one year of age. So you're drinking something your body is not designed to drink.
As to being water...mammary glands evolved from sweat glands, so yes, you are basically drinking cow sweat when you drink cow milk. Um um, yummy. And of course, you're depriving a calf of sustenance. And, cows have been so heavily bred over the years that if they're not milked regularly, they're in great pain from the "enhanced" udders."
I would argue the reverse. Humans have been drinking cow's milk for about 12,000 years, and the consumption of it perfectly tracks the advent of human civilisation (the transition from nomadic lifestyle to a society which remains in one place permanently, requires agriculture including a dependence on cattle)
Genetically, we are in the process of adapting to cow's milk. Most Westerners are genetically adapted (they have the gene for the production of an enzyme to digest lactose) and can digest it very well with no ill effects, while a few cannot.
Unfermented soy products like soy milk were invented in the last 50 years by US agribusiness. The human body has never seen anything like them, and they are toxic in numerous ways.
Interestingly, Asians, who have used soy for thousands of years, learned that it must be fermented to make it safe to eat. (ie, Tofu)
Here is an article discussing some of the ill effects of soy milk. Think of it as drinking a chemical byproduct of GM soy production.
The Truth About Unfermented Soy and Its Harmful Effects