Think holistically

Ourselves, other people, other animals, our mental and physical health, the environment - all comprise one 'substance' ethically-speaking. (Nature is the word I'd use.) I think if you try to see nature holistically like this many moral 'issues' resolve themselves. The notion of self-interest collapses if you act in accordance with nature, because to act against nature is detrimental to yourself.

In this context, living non-violently is the project - of which veganism is, or should be, an important expression.