Yes, HR acts in the company's best interests, not yours. However, if you ever want to be able to pursue legal claims against a company for actions such as permitting harassment, or firing you in retribution for it, you need to be able to document that you reported the problem to the appropriate people (i.e. HR).
Going to HR is the right move for something like this. In any sane company, HR will take such a claim seriously because the potential legal downside if they don't is an unacceptable risk. In an insane company - aside from the fact that you can't measure the insanity level until you have in fact made such reports to HR and seen them dismissed - you still need to be able to show that you brought the problem to HR's attention and they did nothing about it.
Going to HR is the right move for something like this. In any sane company, HR will take such a claim seriously because the potential legal downside if they don't is an unacceptable risk. In an insane company - aside from the fact that you can't measure the insanity level until you have in fact made such reports to HR and seen them dismissed - you still need to be able to show that you brought the problem to HR's attention and they did nothing about it.