Ideologically, women and men should receive the same pay. Not all women do the same job nor do they work the same hours. The reality is that a large proportion of women prefer a better work-life balance. The choices that women make are, on the whole, very different from those of men. This means that outcomes are equally very different.
Source: The Gender Pay Gap Says More about Preferences Than Sexism - Foundation for Economic Education
I'm not going to tell you that sexism doesn't exist in the world because it obviously does. However, that doesn't mean that every statistical variation between men and woman is the result of sexism. Most of society automatically assumes that when a statistic comes along that shows that men have it better off than women in some way (for example, the supposed wage gap) that it must be the result of sexism. This is just absurd. Do most people honestly believe that those in charge of hiring sit around and say or think things like "if we hire her, we don't have to pay her as much as a man" or some such nonsense? I'm sure that it does in fact happen, I just think it is relatively rare, not all pervasive as some would have you believe.
This article goes into detail on the various causes of the "wage gap". Primarily, it comes down to different choices, on average, between men and women. Women, on average, have certain preferences when looking for employment that lead to lower wages. The end result is that women more often have jobs that are more flexible achieving a better work/life balance than men. The downside is that average pay is lower with those priorities. Let's stop jumping off the cliff of assumption at the first chance and look at more of the picture than the tiniest puzzle piece.
And why don't i see any protests about the lack of women roofers?