""The Asian cultures have been eating fermented soy products for thousands of years.""
Why didn't they eat unfermented soy up until recently?
Cooking achieves most of the same goals as fermentation as far as destroying potential problem compounds. The advantage of fermentation is longer storage due to the acids formed, which kill pathogens that can spoil food. It also cuts down on the bloating some people experience from the high alkalinity of the soy. For example the bloating some people and animals experience from TVP can be countered by the addition of an acid to counter the alkalinity. So to answer your original question the answer would be the soy was primarily fermented not only for safety but also for longer term storage just like pickling vegetables. In modern times this is not as much of an issue since we now have things such as refrigeration for storage, so the acids of fermentation are not really needed.