It's just virtue signaling (and I don't mean that in a pejorative way). It doesn't matter that everyone knows HR isn't there to protect you. What you're really saying is "I share your beliefs".

I think probably most people believe that if they have a dispute with another employee that HR will resolve it in a “fair” way. But of course HR is only really thinking of which outcome is less likely to involve lawyers or a tribunal. Head on over to workplace.SE to see loads of this... if you can’t bring a credible threat of a lawsuit HR will always side with your boss, no matter what he or she has done.