In some instances or regions, a majority of male dairy calves are indeed destined for veal production. The dairy industry faces challenges in finding economically viable uses for male calves since they don't produce milk. As a result, many operations choose veal production as a way to utilize these calves.

If we say for sake of example that in some cases, only a small percentage of male calves of dairy cows are used for veal (when largely it is the majority), that's still billions and eventually trillions of baby animals killed in the long run. Also, many are killed upon birth and not even used for veal but simply discarded or used for other purposes ( https://www.theguardian.com/environment/2018/mar/26/dairy-dirty-secret-its-still-cheaper-to-kill-male-calves-than-to-rear-them ). The ones that are raised and killed for beef at a few years old still wouldn't be if the dairy industry wasn't breeding these animals in the first place. And they wouldn't be separated from their mothers, be mutilated, or face a number of other cruel practices.

The bottom line is that the dairy industry causes harm and suffering to animals, including supplementing connected industries like veal and beef, which many people justify as a way to minimise waste of necessary byproducts of the dairy industry, while ignoring or overlooking the fact that the dairy industry itself is unnecessary.

That is clearly a logical fallacy, whereby someone justifies harmful actions as a necessary component of an in fact unnecessary larger set of actions. If you would focus on the actual question at hand, instead of making a tirade against the example I used.

By the way, I think it might be called a false necessity or false requirement fallacy, but that may not be widely recognised. It's related to the more general false dilemma/false dichotomy fallacy I described earlier, but also could be described as a fallacy of composition:

"The fallacy of composition happens when someone assumes that what's true for parts of something must also be true for the whole thing. Basically, they think that if each piece has a certain quality, then the entire thing automatically has that same quality, which might not be the case."

In other words, assuming that because one aspect of something is required as a component of that larger thing, the whole thing itself must also be required, when that isn't necessarily true.