Getting straight to the point, man do quite a lot more for women that women do for man. We take you out on dates which we pay for. We take you on trips and we pay for these as well. We buy you nice things like jewelry, flowers and other types of gifts, sometimes even cars, etc. we give you a place to live, we cook for you, we help you clean. We fix things for you, we open the door for you, we hold your hair while you puke. None of this comes cheap.
Another part is that even when a man pays for every single thing, when things go south and the wife finds a new guy she is entitled to half of everything she never worked for. How is this fair? The only inequality I see is that guys are slaves to women.
So as long as women do not agree to share all these costs I do not think they should be making as much as guys do.
(I know that this may very, some guys are just takers like most women)