As a woman, I'll repeat: paying women less for being women is not despicable.
That doesn't mean it's good. It's bad. But it's normal and there are a lot of social forces at work. Good, well-meaning people have all sorts of logical reasons to pay women or minorities or handicapped people less. You don't have to be evil to participate in a sucky system. We all do, even the virtuous ones. So, open your eyes and work to change things.
As long as we frame bias as something only despicable people have, we will not be able to change anything. After all, we're not despicable, so we can't be biased! Yay. False. Bias is something good people are still steeped in. It's how humans operate.
Transparency in pay is a way in which good people can be confronted by their bias. In any one situation, you can argue that a woman deserves less (rationally and justly -- just change the rules for evaluation so she loses [1]). If via transparency and use of data you notice that women are consistently paid less, and that your evaluation criteria keep changing, you can realize your implicit bias and change your actions.
[1] http://advance.cornell.edu/documents/ImpactofGender.pdf , http://www.ncbi.nlm.nih.gov/pubmed/9120783 .