I'm responding directly to an argument based on it being morally wrong to kill living things, specifically to kill some living things but not others (cows but not golden retrievers).

I am not making arguments against veganism, i am asking a philosophical question in response to a moral position. Please understand i am not attacking you or your lifestyle

My argument was, again, how do you use a moral justification of 'killing things is wrong' to change from one lifestyle of killing things, to another lifestyle of killing different things?

Why is cow vs golden retriever so important, but golden retriever vs potato completely laughable? You are still ending life to nourish your body no matter what. Both a cow and a potato cause and have external costs as well (i would say methane from cows is less or equally concerning as pesticides)