Well, it's a complex issue, and it's going to take a complex answer to respond to it, I suppose.
First off, and I know it's been reiterated by pretty much everyone above me, but the presumption of innocence is a legal standard, not a moral or ethical one. I as an individual or as a member of society do not have to wait for someone to be tried and sentence before forming an opinion of them. To take the most extreme example: Bill Cosby is an asshole of the highest order. I think we can all agree on that. I think we can all agree that he should be judged morally by members of society for his actions, despite still being "innocent".
Secondly, I do believe people should wait for evidence before making up their minds, and that works both ways. I think it should be pointed out as well that victims who come out face as much if not quite a bit more grief than the accused. I personally never jump in on he said, she said kind of arguments aside from sometimes saying "screw him/her if true", which implies I'm not yet sure if it's true or not. However, I have no problems looking at the evidence of a crime and judging the person being accused or not.
To use the example of sexual harassment, abusers rarely ever act only once. There is almost always a pattern of behavior that forms and at that point there are quite a few people willing to testify to that. We can also look at a persons behavior and response to any accusations to determine how we feel about an incident. And yeah, when it's murky, I'm not going to blame people one way or another for coming to a conclusion. I personally try to stay out of it until there's enough evidence one way or another. But again, that given sufficient evidence, we as individuals can choose to judge people and organizations, despite being not guilty.
As an addendum, to see what happens when presumption of innocence gets thrown away (legally), look at a coutry like Japan, which has something like a 99% conviction rate. That's why it's important to frame innocence until proven guilty as a legal issue first and foremost. It still is quite important in many places around the world.