Lets do a little common sense here, I am a hiring manager and just interviewed two people with very similar qualifications, backgrounds, and work ethic, but one of them I can save ~20% on pay/benefits.... Wow, I wonder who I am hiring...
It's not pure crap, but you can explain it using market theory because the assumption here is that all other things are equal when they are not.
At any point in a womans career she can fall pregnant, whether this was planned or not. This means that at any point the employer is on the hook for maternity leave which is typically much greater than paternity leave. So given that disparity, if you had two otherwise equal candidates and decided to use economics as a tie breaker you would either choose the male candidate and not take the risk of maternity leave, or choose the female and hedge against the risk by paying her less.
I would expect that focussing purely on equal pay without accounting for this will lead to other effects, like less women getting hired, or promoted which isn't exactly what you'd call equality.