To be fair, the $0.77-gender pay gap is itself close to faith-based - which makes calling the opposition 'faith-based'...a little sketchy, one has to admit - at the least, I've never seen a single study that actually has anything akin to evidence of it existing, ie there being such a gap ($0.77, and that that gap is there due solely/primarily to gender (ie not secondary reasons, that are in themselves non-sexist/discriminatory). In fact, most data I've seen that "supported" that number, in any sort of general sense, has been straight out atrocious - they didn't even attempt to show that it was, just ignored testing for more than a few relevant factors (such as individual salary negotiations, for example), found a difference in the ones they did test for, and then attributed the entirety of it to gender.
Something that every scientist, obviously, would find to be an absoutely hilarious (or rather, completely outrageous) practice, if applied to their own field (I for one could easily show that I've found the cure for cancer, tomorrow, with that approach). This not being what should be refered to as science, obviously doesn't change the underlying premise. To be taken seriously, a study needs to uphold certain standards, and needs to be able to show evidence for the conclusions that are drawn. If not, it's not worth the paper it's written on, and opinion pieces are uninteresting - after all, I think almost everyone already agrees on a gender pay gap being an utterly ridiculous concept, that is a relic of different past.
(just as a side note, around here, the better studies I've read actually places the gender pay gap at a few percent - which is still too much, mind you, but nowhere near $0.77 (granted, though, we're expected to do better than the west as a whole in this regard)).
Edit: To clarify, I'm not trying to say that there isn't a difference in what men and women get paid, I'm saying that the evidence of it being primarily or mainly due to the actual genders of people, is atrocious at best. At least in regards to numbers anywhere near $0.77.