It helps anybody who's underpaid. One being underpaid doesn't imply or even suggest that one was discriminated against. I was underpaid my first job, and it wasn't due to discrimination. I would imagine that the majority of people who are underpaid are underpaid not due to discrimination, but due to poor negotiating ability, lack of awareness of the market rate, etc.

My analogy of "we're raising the minimum wage to help women/<insert minority>" still stands.

Also there's evidence to suggest that the gender gap is a myth http://freakonomics.com/podcast/the-true-story-of-the-gender...