Hard to know what to say regarding the Shukan Post's full-scale attack on women-only train carriages. Read and consider.
The attack seems to have been brought on by Japan's railways providing female-only carriages to alleviate the problem Japanese women have with gropers- known as chikan in Japan. I have personally had experience with this, as a friend and I once threw one of these morally diminished individuals off a electric streetcar.
Personally, while I think that the only real solution to the problem is to alleviate the over-crowding that allows such despicable behavior to occur, I don't really have a problem with female-only carriages as a temporary fix. Of course, I no longer have to ride the Tokyo commuter trains either, so I do not have first-hand experience with their crowding. Anyone else want to weigh in on this?