WTWizard " Even with vitamin B12 supplements, there are other nutrients found only in animal products that humans need."
I'll start off by saying that I'm not vegan or a vegetarian, but I do know that vegans can be perfectly healthy. B12 can be found in many fortified cereals or even nutritional yeast (it tastes sort of like cheese dust). A newly minted vegan has up to 5 years to get a clue about what healthy vegan eating is before their B12 reserves run out. Even omnivores can have vitamin deficiencies if we don't eat a healthy diet. It's just easier for omnivores because we don't have to think about what is basically healthy for us. We learn it as children. I'm sure that someone raised as a vegan would be perfectly aware of the need for B12 in their diet - just like us omnivores know about eating our vegetables.
*however - saying all animals will be vegan is just dumb