extreme diet?
i can't imagine why veganism is an extreme diet when it consists of eating a variety of fruits, vegetables, and other non-meat, non-dairy products. the only supplement you will need is b12. i take a general supplement to make sure i get everything i need, but i was taking that even before i became a vegetarian. in my opinion, that is just good sense.
extreme diets are any that lack variety. a carnivore eating mcdonald's hamburgers every day, or someone subsisting on rice alone will face horrific health consequences (obesity, beri-beri, etc.). being a vegan doesn't make you extreme. eating unhealthy (in any manner) accomplishes that.
instead of bashing mcdonalds, vegans, or meat eaters, if we all are careful to moderate our caloric intake and eat a variety of foods, then we'll be a lot healthier regardless of our dietary philosophies.