I think everybody's all for more women in the work place, and even tweaking some things to make it a more inviting place (but I'd fall short of "catering to" since I don't like discrimination). Stuff like improved parental (both parents) leave, more flexible hours, better work-life balance, etc that helps everybody, but women tend to value more highly and so it disproportionately keeps them away.
Let's say you're an employer with a mostly-male (at least in a particular section) workforce and you want to improve your gender balance in that particular section. Maybe your interviewers have been unfair, maybe the labor pool has been lacking, maybe your offering is disproportionately unfavored by women, whatever - you want to address it because you're progressive and want to do the right thing.
Now you may have some "male chauvinist pigs" in your workforce. You're fine with firing them - you just don't know who they are yet, since there haven't been any women around. There's a risk that you (or your employee managers!) may be held personally liable if some incident go south, and nobody's thrilled with that, but you institute procedures and brush up on harassment law and train people so you're not too worried about that.
But then you read about bullshit like the Adria Richards case and other horror stories that you hear about all over the place from your business buddies and you realize that you're making yourself pretty vulnerable in a way that you can't really defend against. Even excluding the legal issues (you're being sued by an employee...), there's massive PR issues because the kind of personality that tends toward frivolous or over-blown claims is probably well correlated with the kind of personality that enjoys a large social media reach (my observation - may have selection bias, but not really relevant to my point). And neither the law nor the public opinion will give you the benefit of the doubt.
So I don't think there's any denying that a company exposes itself to greater risk by hiring a woman instead of a man. Frankly, men don't really sue for sexual harassment (they should, though, it's not uncommon for men to be harassed). Your progressive employer who's trying to do the right thing will still have to weigh the costs and benefits and determine that the benefits outweigh the costs, or that the cost is acceptable.
The problem is that this should be a slam dunk win for the company - there should be no risk at all for hiring a woman! More generally, you don't want to make the "backwards" viewpoint supportable at all, or else it'll greatly hamper progress on those issues.