Y'know, I keep hearing things like this.
My gut reaction is that there's only one kind of reaction that's really relevant. If Ms. Willis had decked him; would people be less likely to grope her in public, or more so? Would they be more likely to be more physically respectful of other women in public, or less so?
I realize it may sound cheap of me to talk about what the right thing to do would be, since I wasn't there; but I have been in a similar situation, and I have to think that the right thing to do would be whatever would be most effective at cutting down on that kind of behavior in the future overall, no matter whether it got boos or cheers in the next five minutes.