Who's actually to blame for gender pay inequality?

Weeks ago on Twitter, I joked that we could land on a comet but that we could never get pay equality for women. With this note, I posted a meme about how women are like men, only cheaper.
Although most agreed with me, some men and women pointed out that the 77 cents to the dollar gender pay gap is a myth, a fudging of the numbers, which does not compare what a man and a woman make in the same role but what men in total make to women in total. They pointed out that  women make less because they don't enter STEM fields, where the real money is. That they choose their families over their careers, thus resulting in less hours put in or time off that sets them back. That they get paid less because they don't negotiate their salaries. A chart from Top Management Degrees that I've posted below illustrates some of their arguments, and I can't deny that the facts are compelling. Most women do make less money than men, we can all agree on that, but before we cry out that it's because of blatant sexism, we should examine our choices and why we make them first.
Women Don't Make Less
Source: TopManagementDegrees.com