Anyone who raises issues is a potential liability risk, so HR is naturally inclined to work people who frivolously raise issues out of the company. Same thing for raising issues in inappropriate ways (e.g. a twitter thread).
At the same time, if someone above you is a /real/ risk, many HR departments do want to know about that. If your boss is sexually harassing women and acting racist, they're a liability to their boss and the company as a whole. Taking bribes? There are ways to manage that through most HR departments.
Most companies have trainings about the types of issues which ought to be raised, the contexts, and how. This is not a general rule, but for my current employer, I think the training is spot-on for what's expected of employees here:
* Raising issues appropriately is exactly the expected thing to do.
* Following up, and expecting they get acted on is not.
HR expects to be able to conduct a discrete investigation. If there isn't evidence, one should expect that nothing will happen except for a paper record. If you were sexually harassed by a manager, but it's a he-said-she-said, that's where it ends. Once a few employees claim they were sexually harassed by the same manager though, that person will be gone.
That's my current employer. I've seen this all over the map. My previous employer, I'd recommend /never/ going to HR.