Soy contains phytoestrogens which lead to some sort of hormone imbalance that has negative health effects.
Interesting that if you just start typing "soy estrogen" into DDG, the first suggestion is "... myth".
"Phytoestrogens" have "estrogen" in the name just like "methanol" (which will kill you) has "ethanol" (booze) in the name. Analogous molecules with similar names don't have matching or identical functions, and one molecule can be hundreds of thousands of times more potent than the other.
There is no serious correlation between estrogen levels and soy consumption beyond random noise.
Estrogen is a significant threat to the environment and are released in large part by animal agriculture (remember, most farm animal populations are female-biased due to the production of eggs and dairy, as well as general animal husbandry).
Estrogens are present in eggs, dairy, and meat - and their levels, adjusted by the potency of the molecules, are significantly higher than soy. Thus if you are truly concerned about estrogen levels, please avoid these foods.