I actually did a lot of research on this at one point. I wish I had the time to brush up, but I'll give my $.02 on what I remember.
1) Traditionally Asians did not eat as much soy as their reputation suggests which would mean that there may be other explanations for health benefits usually attributed to soy.
2) A significant amount of soy that was traditionally eaten in Asia was from fermented soy products. Here is a link to an article that gives an overview of the health effects of fermented versus unfermented soy. To summarize very briefly, fermented soy is better. http://www.mercola.com/2004/aug/4/fermented_soy.htm
To the extent that previous generations of Asians were healthier because of soy, it is probably because they ate fermented soy. Unfermented versus fermented soy products are listed below. My guess is that the average American eats mostly unfermented soy products.
UNFERMENTED SOY PRODUCTS: Fresh green soybeans, Whole dry soybeans, Nuts, Sprouts, Flour, Soy milk, Tofu
FERMENTED SOY PRODUCTS: Natto, Miso, Tempeh, Soy sauces, Fermented tofu and fermented soymilk
3) American soy is typically genetically modified. As far as I can tell this is more of an agricultural issue since the genetically modified soy has somehow created pesticide resistant weeds. But there may be health implications for regarding the composition of the soy that modern Americans are eating compared to the soy traditionally eaten by Asians.
4) Small to moderate amounts of soy are probably not harmful. However, there is a lot of "hidden" soy in packaged and processed foods, including
--oddly engough-- some meats. E.g.: lecithin, "vegetable" oil, textured "vegetable" protein, etc. So, unless your diet consists mostly of "whole" foods, you are probably already consuming more soy than you realize.
Keep in mind that soy is now big "agri"business. Many of the positive studies about soy were probably commissioned by this Industry. However, you don't need to look hard to find negative information. Just go to a metasearch engine like "Dogpile" and do a key word search such as "soy negative effects".
I don't have a strong opinion one way or the other since even though DD is dairy intolerant there are plenty of other good sources of protein so I don't feel the need to research the issue more carefully, I simply err on the side of caution and avoid most soy, except for the "hidden" soy in processed foods. Especially since a significant percentage of kids that are dairy/cow milk intolerant are also soy intolerant.