I try not to think about the topic too much because I like the occasional spot of cheese, but the number of calves that get slaughtered each year to enable milk production is mildly disturbing. Even worse, some countries have regulations against selling animals under a certain age, and the milk's worth more to a farmer than the month-old calf, so you end up getting piles of male calf carcasses thrown into pits for composting.
That's if you merely think about the concept for a moment. If you bother considering it any further or make any effort to consider the cow's (mother's) experience, you should (if you're not a sociopath) find it far beyond mild disturbance.
Death itself is wasteful but isn't as tragically unethical as the specific aspect of taking a mother's offspring away, which hits perhaps the most powerful low-level aspect of mammalian experience. That we then go kill them is appalling in a human principle (in that we understand the whole picture). Killing them in front of the mother would be a further level of horror that I assume doesn't typically happen (Aside from the gratuitous torture, I bet that would increase cortisol levels in the milk).