Why do we need animal protein to build muscle. A gorilla, an elephant is composed of far more muscle mass than any human all built exclusively from plant protein.
And, of course, both gorillas and elephants have the exact same digestive systems as humans do right? LOL
Well, practically speaking, the only plant-based protein powder available is soy and I would be very cautious of that if you are a male. Soy is tied to brain shrinkage and other problems for males. Better to wait about 20 years and see what the research turns up than to risk your precious grey matter. In general, phytoestrogens are very hard on the male body and soy is full of them.