Jaqui, could you answer this:

Most women's advocates seem to believe employers are fiercely determined to pay women less than men for the same work. 

Yet they also seem to think employers' prime modus operandi is greed. ("Corporate greed" is perhaps one of the Left's most salient rallying calls.) Thus they no doubt believe employers would hire only illegal immigrants for their lower labor cost if they could get away with it (many do get away with it), or would move their business to a cheap-labor country to save money, or would replace old workers with young ones for the same reason. 

So why do these same feminist activists and women's advocates think employers would NOT hire only women if, as they say, employers DO get away with paying females at a lower rate than males for the same work?

See:

"Salary Secrecy — Discrimination Against Women?" http://malemattersusa.wordpress.com/2014/10/27/salary-secrecy-discrimination-against-women/