I have never been accused, but I am certain that I could not be found guilty of sexual harassment

Well, this is probably because you are certain that you would have witnesses.

But, many men have been sacked, and then discovered that their witnesses were not even interviewed. Are you still confident that you could prevail against a liar, if your witnesses were not interviewed? Remember, the woman potentially has the financial resources of the US government behind her to fund a legal case against the employer. How much could you afford to spend. Very little in comparison to the US government.

What happens if a liar could use a false accusation to deny you a promotion while she gains one or removes a competitor.

Which would you do if one of your colleagues was accused, (and you were sure he was innocent) would you risk the wrath of the HR manager to help him. Would you help him to sue your own employer. Seriously? And would he do so for you if you were accused?

How is your colleague going to react when the HR manager looks him in the eye and says "I conducted a thorough investigation and concluded there was wrongdoing - though there is no proof" If your colleague chooses to help you in a legal case he is effectively choosing to believe that the HR manager is deceiving him, isn't he? That would upset the HR manager. Are you sure that your colleagues would choose to announce that they trusted you more than the HR manager.