Lets say you see a moral wrong that others ignore, often while admitting that they're wrong to do so, and you alone act against that moral wrong despite it being hard and being mocked for your decision. How else would you feel? If you felt that being vegan was morally equal then you wouldn't have become a vegan for ethical reasons in the first place. So by definition, you must believe yourself (in this specific area) morally superior, and based on that one data point, it's probably safe to generalize that you're morally superior to the majority of non-vegans, just like how you probably consider yourself morally superior to people who litter or hit their kids.