Veganism/vegetarianism are both already series of arbitrary lines drawn, though, so, whatever.

They are not fixed lines. I can’t speak about veganism but not eating red meat is vegetarism, leaving meat out except for holidays is vegetarism, eating fish but not meat is vegetarism. There is many way to be vegetarian. Even if there is one way that is much more popular and much more discutes these days. So I can also image non-fixed lines in veganism.