I'm not saying to fire people as soon as someone gets accused. But any victim DOES have a right to be believed; there is no way to differentiate a false accuser from a genuine victim initially, is there?
The firm needs to do their homework behind closed doors and figure out who's telling the truth. Get testimonies of employees, examine digital evidence, use lie detectors, etc. If evidence is conclusive, fire the accused. If it's found to be completely false, fire the accuser and exonerate the accused to your other employees.
Sexual harrassment needs to be punished, but so too do false accusations. There is no double standard.