Equal pay for equal work, at the end of the day, is an incredibly low bar to set for gender equality. I would get equal pay for equal work at a sweatshop in China, but a sweatshop worker by no means has the same income opportunities as I do.

Gender income inequality is a matter of opportunities. It happens at the education level, where women are less likely to be encouraged to go into higher paying fields, at the hiring level, where equally qualified women are less likely to be hired for the same job as men, and at the promotion level, where women are less likely to ask for, and be taken seriously when asking for, increased position. Looking at salary differences after all these effects takes the real issue of opportunity differences, and replaces it with a non-issue of salary differences within the same position.