No, I don't want to abdicate responsibility. You know me and my stance on these sorts of things and we see eye-to-eye in that regard.
But the smart thing to do in the bus case is to acknowledge the victim's situation vocally if you pick up on what's happening. That alerts everyone else, including the driver. Then, if you feel it's the right thing to do, communicate to the victim to move and if you so choose, get between her and perp. Call out to the driver to stop the bus, that it's an emergency, and you then instruct the individual to leave the bus immediately while dialing 911. The last resort should be physical contact of any kind.
But notice that in that article nowhere does it mention other passengers were made aware of the incidents. Now I have read some of the online commentary and one person did say she brought the issue to the attention of the bus driver who said something like "yeah, this guy does weird stuff all the time."
My own daughter was one of the women who came forward. None of what has been said here would have applied in this situation. His behaviour was not obvious to anyone. It was very subtle. So subtle I had a hard time understanding what he was doing when my daughter texted me and alerted me. I was sitting on the same bus! Most people on the bus are wearing earbuds and staring at their phones. Thankfully the power of social media and the actions of Vic PD this ended in him being arrested. Far quicker than I expected.