Ethics of veganism falls down if they lose the health wars--even just trying to convince somebody of their own free will to go vegan becomes less ethical, if that person's health is likely to suffer as a result. I'd sacrifice a cow's life over my niece or nephew's health, any day. If somebody did some version of veganism and their diabetes went into remission--and I think this does happen, sometimes--I'd never try to convince them to change their ways, if that was working for them, although I might encourage certain supplements for nutrients that are going to be low on a vegan diet.