As I see it, the danger to the fish population is that if too many fish undergo some type of sexual transformation, normal reproduction patterns and processes will be altered.

As other posters have pointed out, male/female sexual characteristics aren't as "hard-wired" in fish as they are in mammals. For example, all groupers are born female but some undergo transformation into males at a certain point in their development. How many undergo this transformation depends upon the ratio of males to females within the adult population. Both males and females excrete hormones into the water and a "female heavy" mix promotes more female-to-male transformation. But once enough fish have been transformed into males the hormonal soup becomes "male heavy" and transformations cease.

Smallmouth bass and other sunfish don't ordinarily exhibit this sexual transformation capability but it's probably not buried too deeply within their genetic makeup. The observed transformations within their populations is due to chemical pollutants mimicking hormones. The problem is that such transformations stimulated by natural hormones cease when the proper male/female balance has been achieved. Artificially introduced hormones, on the other hand, have the capability of stimulating sexual transformation within the entire population of an affected area, thus rendering reproduction impossible. If all the female fish turn male, who's going to lay the eggs?