Well, I now know the sources of why some Jewish women cover their hair and skin, as well as the source of "kol isha." However, I'm not convinced that these restrictions are blanket statements about all women. It's not entirely clear, but it could be argued that these statements are contextual, referring only to a man's wife at the time he needs to say the shema. In other words, hearing the voice of a woman is not a problem because it may be seductive. Rather, if I hear my wife's seductive voice while I am trying to say the shema, that may distract me. An even strong example – if my wife's hair, legs, or full naked body is right before me, then clearly I would be distracted from saying the shema. But seeing a random woman's hair uncovered while walking down Broadway, not during davening? Maybe that's not what they're referring to.
Where the boundary is, however, is not terribly clear. For more investigation...
