There are two ways to approach this topic from the Pro side and I will do my best to condense both down in the First Round.
There is the moral argument and the legal argument. The moral argument is that it is right from the side of nature. Ultimately we are a part of a food chain. Our technology and the intelligence that birthed it have caused us to have a distorted presence on the food chain from a biological perspective but we are a part of it all the same. Fundamentally, as living organisms we have to live off of other living organisms to survive, whether or not they are part of the animal kingdom becomes a semantics argument that is based entirely off of emotion.
The legal argument is that since most domesticated animals are created by the means of human beings who intend to consume them or use them for natural resources, it is the right of a human being to consume them. You also have to realize that domestic animals do so much for humanity and consuming them has sustained the lives of tens of billions of human beings for thousands of years.
Yes I understand that it is in our nature, but there are actually animals that can make us sick. Such as pork, from what I have recently learned it has a certain kind of germ that can not be killed off. Also yes I do know that vegans have to take many different supplements to get protein and other things. There are other things out there to eat, and we can get protein elsewhere.
There are so many animals dying at such a young age and its not fair. They can live so much longer than just a few months. Animals can live up to years but instead they are being slaughtered as babies for food. I just don't see how that is fair. Why can't we give them a chance at life. I also don't understand why they are being slaughtered for milk and such. Just because they suddenly can't provide what we need doesn't mean they are worthless. Not to mention that the exotic animals are being skinned just so people can wear them as coats and shoes. A lot of those animals are being extinct because of this. Thousands of animals are being killed for food and material, so what happens when there aren't anymore of these animals to consume?