I apologize for being harsh and accusatory, you do seem to be looking at things in good faith.

When it comes to moral rules, I'm less concerned with universal rules that apply to all theoretical cases without exception and more concerned with establishing good guidelines. Generally, it's always possible to find some edge case or hypothetical where a rule may be questionable. In those cases, you just have to use your best judgement. But it's useful to use your judgement to establish general rules that apply to most cases, because realistically you're not going to reexamine everything each time you go to the grocery store.

thevegansociety.com defines veganism as:

Veganism is a philosophy and way of living which seeks to exclude—as far as is possible and practicable—all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose; and by extension, promotes the development and use of animal-free alternatives for the benefit of animals, humans and the environment. In dietary terms it denotes the practice of dispensing with all products derived wholly or partly from animals."

"As far as possible and practical" should clear up certain things, like the idea of starting wars to liberate animals. Killing farmers is not a particularly effective way of advancing the cause of veganism, extreme ethical positions aside, it discredits the movement, and it tends to impair one's ability to advocate for change. Likewise, I'm not going to go visit an Inuit tribe and try to convince them to go vegan when there are people who are physically and culturally closer to me who are causing more harm.

There is a pretty wide gulf between a thing being morally wrong and a thing being a capital offense. I can't speak for others, but generally if I draw comparisons to slavery or genocide, it's not attempting to draw a moral equivalence, but rather trying to show a logical inconsistency in someone's argument. Some arguments against veganism, if followed to their logical conclusion, could be used to justify things like slavery just as easily, but that's not the same as saying the two are equally bad.

Applying absolutism to any moral principle tends to produce unreasonable and impractical conclusions. As they say, only a sith deals in absolutes.