There are valid concerns about soy, but only in certain situations.
Soy is a concern for the hormone-sensitive type of breast cancer, but only if you already have the cancer. Eating soy has not been shown to correlate with an increased risk of hormone-sensitive breast cancer. Your biggest risks for breast cancer are being female, old, overweight, etc.
Soy consumption hasn't been shown, as far as I know, to be correlated with the incidence of prostate cancer. A few foods, such as pomegranate juice, have been shown to reduce the risk of prostate cancer, and perhaps help fight the disease.
Soy consumption has been shown to correlate with increased incidence of senile dementia in later life.
The emerging picture is that people are now eating soy in far more forms and greater quantities than ever in human history. What if any significant epidemiological effects this will lead to remains to be seen. For now, eat soy in moderation (a couple times per week), and avoid it if you develop breast cancer.