The most powerful argument I've encountered for ethical veganism is known as 'Name the Trait'.
Its most rigorous and recent iteration - as described by PhilosophicalVegan.com - runs as follows:
P1) If your view affirms a given human is trait-equalizable to a given nonhuman animal while retaining moral value, then your view can only deny the given nonhuman animal has moral value on pain of P∧~P.
P2) Your view affirms a given human is trait-equalizable to a given nonhuman animal while retaining moral value.
C) Therefore, your view can only deny the given nonhuman animal has moral value on pain of P∧~P
('Trait-equalizability' is defined as something like, "If human moral value can be made identical to animal moral value and the result is that humans still have moral value, that reveals that animals had moral value all along").
Whilst the source for the above material is clearly biased, it does deal with attempted refutations. Whether the refutations mentioned are are adequately addressed and whether there are others that have not been addressed is not clear.
All this being said, it is far more common for the 'Name the trait' argument to take on a more colloquial form, which is usually posed as a question typically expressed as something like:
"What trait(s) do non-human animals possess or lack which justify their torture and killing?".
Given that this is the form the question most often takes in casual settings, I am very interested in any responses and justifications. The question essentially asks how the torture and killing of other animals might be justified given a consistent application of the views which govern how we treat our own species. It is a question which provokes contemplation of one of the most pressing ethical issues of our time.
During in-person debate I have never encountered any successful naming and defending of a trait. A typical, fairly hasty response would be something like, "Other animals are less intelligent", to which one obvious retort is to ask, "Are we then justified in killing a human who does not rise to a certain level of intelligence? If so, what is this level of intelligence?".
Among the traits which might be named are those listed by PhilosophicalVegan.com. I have duplicated them below for quick reference, via links which summarise and provide refutations of the argued-for trait.
Species maximum, Species normalcy, Has moral value, God's Permission, Soul, Legality, Social Contract, No Reciprocation, Group Membership, History/Tradition, Bred To Die, Food Chain/Naturality,Not Human, Low Intelligence, Civilization/Culture, Moral Agency, No Personhood, Sapience, No Technology, Dignity, No Potential For X, Utility, Nutrients, Quality Of Life, Pleasure/Preference/Whim, My Apathy/Nihilism, Futility, Mathematics, Language, Literacy, Unspecified Differences, All Exact Traits