Earlier quoted context omitted.
But the problem is "know what they are doing" can still be unfair. Consider: you're staffing up a company and need folks now. You've found two candidates who seem equally qualified and want to hire them. Both are asking for only a modest raise over their current salaries, but one happens to make 50% more than the other due to arbitrary reasons[1] having nothing to do with qualifications. What do you do? Realistically…
And if we change [1] to "Yeah, one is a gal", then I'd expect a lot of pro-diversity people suddenly stop complaining that there's a problem. Ultimately, the only alternative is to pay people equally. Which won't fly generally, as companies always want to pay the minimum amount that can keep the employee from leaving.
Find me someone (anyone, anywhere) who defends (even in the abstract!) a situation where women are paid more than men for the same work. That's a horrific strawman, and it tells me that you're looking at this as a war (with feminists as your "enemies" I guess) instead of a problem.
And no, you don't have to pay people equally. You have to pay them fairly. If there differences between individuals, that's fine. If there are systemic differences between easily classified groups of individuals, that's discrimination.