As far as the murder part goes, dairy cows are mostly all killed very quickly after they stop producing milk. They are almost never allowed to live out their full lives. Especially, none of the cows in the larger dairy industry. The calves produced in the process are also just raised to be slaughtered. Besides the murder, The act of farming dairy products is also just cruel and inhumane in practice.

To produce milk, cows have to be kept in a pretty much constant state of pregnancy. Once the calves are born, they are immediately taken from the mother, and it is known that cows have maternal instincts that makes this painful for them. They have to be taken away, because otherwise they will drink the milk we are trying to steal from the process. Then the calf's are raised in isolation for the first few months of their life on a milk substitute.

That is the bare minimum amount of cruelty needed to produce milk. Obviously, our modern capitalist driven dairy industry ramps up the cruelty in many other ways to increase productivity and efficiency.

Because you can't get consent from the animal you're milking.

Cheese isn't bad in vegetarianism only veganism. One says "I won't eat animals" the other is "I won't eat anything made by animals or the animals themelves."

https://m.youtube.com/watch?v=FvppRx41YDU

You technically could make cheese without murdering a cow but you won't find any made that way. Cows only produce milk for their young. To make milk they need to be repeatedly impregnated over and over again. Lifespan of a cow can be 20 years, though they are usually killed after about 5 as their milk output drops. Half of the cows they give birth to will be male and almost all killed as they don't produce milk. Some of the females may be killed too as you'll end up with more cows than you have room for it you keep them all.

As for a human child, drinking human breast milk is considered vegan as long as it was given consensually. If you kidnap someone and tie them up in your basement then it wouldn't be.

A baby human consuming their mother's breast milk is vegan, because the mother is consenting to it. A cow cannot consent to being forcibly, artificially impregnated for the sake of producing milk. They don't consent to having their horns chopped off. Nor do they consent to their children being stolen from them almost immediately after birth to be butchered for veal.

Yes plant-based cheeses are intended to mimic animal cheeses. But that doesn't mean they have to be identical. Guilt puts a tint on the things we experience, and the way we feel can be considered a dimension of flavor. I would imagine a lot of people would argue they don't feel guilty about consuming animals or their secretions, but that's only because they've never experienced any time without that guilt. If you're used to feeling a certain way every day, you start to forget about the feeling all together, even though it's still effecting you in the background.

The idea with plant-based alternatives is to have all of the good properties of their animal-counterparts, and none of the bad. Cheese that's free of the shame and guilt of causing unnecessary harm and suffering to thinking, feeling, sentient beings inherently tastes better.