[chc]

> Isn't it the responsibility of the people making unprofessional advances to stop

Well, yes, but if your plan to stop sexism is something along the lines of "Wait for jerks to suddenly become good people," you're doing a disservice to their victims.

> and silent bystanders to tell them so

I don't feel like it is my business to step in and speak for a woman who has not implicitly or explicitly asked me to do so. That seems like a really degrading viewpoint. If she clearly wants the guy to go away and he won't, yes, go up and help her. But the idea that it's my job to run around policing women's sexuality is just antediluvian.

[npfmn]

I don't see why it's degrading for a victim to have someone else (publicly or privately) tell their agressor to stop.

[chc]

The assumption of woman as victim when there's no indication that she sees it that way is what's degrading. Can you imagine if anytime you were talking to a member of your preferred sex, somebody came running up and yelled to the person you were talking to, "Hey, back off, buddy"?

[npfmn]

There's a difference between talking and awkward, unwanted, sexist advances. If you can't tell the difference, then you're right, you probably shouldn't tell anyone off. But just because the victim doesn't say something doesn't mean they don't want something to be said.

[chc]

Sure, if a guy walks up to a chick and sticks his hand down her pants, that's one thing, because he's clearly out of control. But the example given in the OP was something like "Would you like to have a drink?" I don't think I would be inclined to come charging to the rescue if I saw that. I don't like that women have to deal with unwelcome advances, but I wouldn't feel right rejecting him for her.