People can also be very manipulative. Following down this path (i.e. "believing that the accuser is right even before the investigation starts") will only lead to less women being hired for relevant positions.
Here's a relevant scenario: I'm a man, I hold a managerial position and I have to choose between hiring another man or a woman as a one of my direct-reports. Let's say both contenders have the same qualifications, they're both equally fit for the job, but then, I, as a manager, start thinking that if I hire the woman she will then possibly think of filing a sexual harassment complaint down the line in order to take my job. Remember the "believe" part, which means that the sexual complaint doesn't even need to be backed by anything real, because most of the times after the complaint has been made public the damage is already done for me, as a male manager, no matter what the investigation finds (if it manages to find anything). So I choose the man over the woman as my direct-report.