There is no question about it I love meat and enjoy it with most of my meals throughout the day. However, I was thinking about some of the strongest animals on earth and a lot of them are vegetarian and won't eat meat. Take for instance a gorilla, vegetarian by nature and design and it is the strongest animal on earth pound for pound. Now arguably the king of all beasts is the lion and that is of course a carnivore, but the fact still remains a vegetarian style diet can still lead to a strong body.
The same is true with other mammals including the elephant, hippopotamus, giraffe, rhino, wild horse and buffalo. They are all plant eaters and get all their protein and amino acids in plants. Obviously there genetics and structure is a completely different topic but there is definitely some proof in nature that vegetarians can get enough protein and develop large and strong muscles.