I think you're barking up the wrong tree.
Even if you think it's all for show, this is a good way for Craigslist to use their ubiquity to lift FOSTA into the public eye. Nobody knows what FOSTA is much less the sort of impact it could have on their day to day.
But I suspect Craiglist's legal team isn't a bunch of idiots when it comes to toeing the line of prostitution. They outlived websites like Redbook even though they have obvious prostitution classifieds. I'd imagine they're experts.
It looks more like the Communications Act of 1934 was the centerpiece of their defense.