I asked my Naturopath about soy when one of the frequent controversies was going on here. He thought soy was fine in moderation. One of the problems is that soy is very common as a filler in refined foods and some "health" foods. Many people are consuming huge amount of soy without realizing it (or perhaps not caring). Doc. would say eat a Bocca burger or drink a glass of soy milk or eat a little soy cheese, but don't do all three in a day, and don't use soy as a major part of the diet everyday. A little soy can be good, even beneficial, but too much can cause problems. Moderation is the key, but isn't that true of almost everything.
Incidentally, that is how I feel about kelp too, a moderate amount is good, but too much can cause serious problems in some people.