At most organizations I've worked for, HR more or less is separate from staff. They were even located on a separate floor in some cases. At one particularly toxic company, the two HR reps got very close with certain staffers. They joined the gossip crew and socialized with them all of the time after hours.
Suffice it to say, when a few staffers started to complain about the toxic climate, HR did little to nothing because their buddies were the source of the toxicity. It was clear they were biased.
For those here who work in HR, is there usually a code of conduct for your department that discourages getting too wrapped up with staffers? I think if my former employer's HR team stayed separate-- their desks were right down the aisle from their buddies' desks-- and did not get wrapped up in gossip and politics, we would have had a healthier workplace.