We're omnivorous by nature, that should be the only argument espoused.

However that argument itself is void since we are an advanced species that has drastically changed how we "hunt" we should be taking steps to reduce the damage done by our farming and going vegan is by far one of the best options (if not only real option).

However the belief that suffering is the reason to go vegan is somewhat stupid to me, purely because studies are showing that plants do indeed suffer but not in a way that we can visibly perceive like an animal. Just because it doesn't cry or whine doesn't mean it doesn't feel pain and thus suffering.

The idea of going vegan for environmental reason I completely agree with, although I personally will not.