All proteins are not created equal. Animal proteins and plant proteins are used differently in the body, and they are not precisely interchangeable.

Protein deficits in children can permanently stunt growth, and cause a specific type of malnutrition, called Kwashiorkor. Parents who dismiss protein needs in children, in support of a vegan diet are playing fast and loose with their children's lives.

In this day and age, protein intolerances are fairly common, but they are often due to the chemicals that go along for the ride, and not necessarily the protein itself. Gluten, milk proteins, bean proteins, canned meat proteins, egg whites, and other protein types may cause digestive upset when an intolerance develops. The majority of the time, it is either reversible, or switching to a different form of the protein (fresh cooked instead of canned, raw instead of pasteurized, fresh milled instead of in pre-baked goods, quail eggs instead of chicken eggs, etc) will allow compensation for the problem.