How does one protect oneself in cases of sexual impropriety then? This seems like a pretty dangerous flaw. To be completely honest I've always felt that HR has been the "police" of the workplace, there to keep issues like this from getting out of control (as it most certainly did in the case of OP). Now I feel much more exposed...
HR's role is to advise management on how to adhere to labor law. Often times they also handle record keeping for legal purposes, including reporting of sexual harassment. But they're not there to protect you. They're there to protect management from itself.
> How does one protect oneself in cases of sexual impropriety then?
Document, document, document. Not because you're going to sue, but because this is rarely a 1-off situation and when the class action comes around you will be prepared with ammunition.
Bosses who harass employees and a culture that encourage such things present a much larger risk to the company than a single employee's complaints, so in a well-functioning company their incentives align with policing these issues. But it's still worth keeping in mind that their incentives are not your incentives, and if they have given up on keeping the company culture healthy, their interests will be oppossed to yours.