HR are on your side when your interest and theirs are congruent and when they recognize that. You'd think that it would be in the company's best interest to avert lawsuits, but that doesn't mean that they act accordingly. My former employer paid ten millions in settlements in the last two years, several lawsuits are being litigated now, and even more suits are coming down the pike.
They're not your enemy, but not automatically your friend either.