- Animal protein is superior to plant-based protein if you consider the natural amino acid profile. Plant-based protein simply lacks several amino acids and many sources aren't "complete" proteins. - Vitamin B12 is essential for the body and found almost exclusively animal proteins. A Vitamin B12 deficiency can be serious over time and lead to some nasty side effects. Of course, you can always supplement Vitamin B12 and eat fortified foods. My personal preference is to get as much vitamins and minerals from my diet. - Satiety. Animal proteins simply tend to be more satiating (at least for me). - Calorie content. It's really difficult to eat the calories needed on a vegan diet. A massive calorie deficit (especially long-term) can wreak havoc on your hormone profile and bring about a number of other health issues. - Animal overpopulation. If we don't hunt certain species of animals periodically, they'll overpopulate. Hunting keeps nature at a healthy balance of which the available habitat can support. The hunting license fees also support wildlife conservation so that we can protect wild animals and their natural habitats. frnkng mentioned wild boars... they serve as a great example of the threat to pose to farms, because they damage acres and acres of crops.
With that said, my diet varies throughout the week. I'll have moderate amounts of meat for a few days and then I'll switch to plant-based proteins for a few days. I find that it's better on my digestive system.