Contrary to popular belief and as a result of very successful marketing, soy is not man's best friend. Not in the least. In fact, soy can be quite toxic especially when it isn't fermented (I think tofu is a fermented product). Nonetheless, soy has always been presented as a health food, with advertisements boasting about how soy is the cornerstone of healthy Asians. The fact is, Asians eat very little soy.
That said, I will be buying soy free feed for my goats. Goats, like humans, are not built to digest soy without negative side effects!