I think it's important not to shun all animal products. For example, organic yogurt has vitamin D, probiotics, and protein, and as far as I know, the cows aren't abused. What's wrong with that?
But if if you are vegan or vegetarian, if you don't have a well-rounded diet, you should probably take a multivitamin. I hear you can miss out on some B-vitamins.
The best thing to do is do your own research - diets can be hazardous if you don't cover all the bases and you can't depend on other people to do that for you.
updated by @tony2: 07/18/15 05:50:40PM