Earlier quoted context omitted.
Why is it the responsibility of women to take the stand? Isn't it the responsibility of the people making unprofessional advances to stop and silent bystanders to tell them so? Why is a professional conference ever even thought of as a venue for making advances? I don't understand why you think this is not sexism.
As a bystander who becomes aware of such behaviour of course it's your responsibility to get involved. But if we're talking, as the article does, about a woman and one man alone in an elevator, and that man happens to be an asshole, what can the rest of us realistically do to prevent this happening?
It's about creating a positive environment. Of course there will be isolated incidents, but can we really resign ourselves to doing nothing?