CellBioGuy isn't (so far as I can tell) trying to force employers to pay women the same as they pay men (that would count as "demanding" and might be unethical); he's merely saying that he thinks they should pay women the same as they pay men.

Not really. If an employer only hires women than it's not about paying woman as much as the employer pays men. There no real reason why the employer who only hires woman should pay them as much as a men would get if he worked for someone else.

If a men applies to the company and is willing to work for the kind of wage women usually get in the market place of course he could be hired.