Soy is a legume that in my opinion is unfit for human consumption.
Soy contains antinutrients and phytoestrogens that affect thyroid function and you don't need it.
Soy protein is just another industrial artificial food product pushed on us by big Agriculture.
It is no substitute for far superior animal protein.
Fermented soy products (miso, natto, soy sauce) are acceptable as a condiment.
Mark Sisson wrote a posting titled Scrutinizing Soy where he basically comes away undecided about the real harmful effects of soy if eaten in whole qualities vs. processed. He eats edamame from time to time but stays away from soy protein as a general rule...read the post.