Technically you are absolutely right. One accused of sexual harassment is innocent until proven guilty. Unfortunately the reality of the situation, at least at any big corporation where I have worked, is that once one employee brings such a claim to HR against another, you can stick a fork in the accused. His or her career is done. Most companies lean heavily towards the accuser if for no other reason that to ensure they can't be included in any civil suit. Since most of these situations are he said/she said anyway, by favoring the accuser they head off the claim that the company fosters a hostile work environment.

Obviously if there are witnesses then that's different. But in a no witness scenario, even if the accused doesn't get fired, they will soon leave on their own. Unless they like no hope of ever having an upward career path.

I'm not speculating on this. I can give at least two examples, at different companies, that I have personally seen.