I’m very skeptical that their motive is hiring discrimination as opposed to cutting costs on ads by targeting the demographic that is most likely to respond to the ad campaign. In other words, if the ad campaign isn’t successful for recruiting women, why would they spend twice as much for no increase in ROI? Maybe they could run a different campaign that targets women, and perhaps they are (if there is something in the article that claimed these employers are only running campaigns that target men, I missed it), or perhaps no one has found a campaign that is comparably cost-effective for hiring women as is the case in STEM fields. I just don’t see what these firms would stand to gain from hiring discrimination and I have a hard time believing they would take a significant financial hit just to be grinches.

Yes, I was thinking about that as I wrote, one imperfect but possible fix would be "no pay per view for job listings". Which, for all I know, could already be the case.

The ads would still be illegal even if they weren't pay per view.

If they aren't pay per view, there's much less incentive to show them to only certain users, and much less burden on the employer to be inclusive.

How did they imply that hiring women is charity?

Nobody would even think to complain if the implication behind this post was that the company was self-sabotaging itself.

To briefly speak of ethical and legal issues, it is highly doubtful that they would have a policy of not hiring women if women actually apply for the position (and that would most certainly be illegal). Much more likely is that whoever ran the Facebook campaign checked off that option in an dumb attempt at controlling ad campaign costs? Or maybe they ran a separate campaign to recruit women? Or maybe some other non-nefarious reason.