It's only offensive for the same reasons it's offensive to continually tell Muslims they should do what they can to stop terrorism.
Men already DO this. This is what we have ALWAYS done. Why is it en vogue all of a sudden to pretend we don't? Or that we have a culture that needs to be changes because it endorses this sort of behaviour? The whole western ethos is BUILT around the idea of good men protecting the vulnerable.
Go back to the 1800's and read Dickens and Hardy. Go back further and read Milton and Shakespeare. Or further yet and read Malory.
Or just remember back to high school when you and your good guy friends (assuming you were a good guy) told the girl that she might want to stay away from that dirtbag that everyone of you knew was bad news... and she couldn't run to him fast enough.
Why are we acting like this is some sort of new message that needs to be voiced?
Better yet, why are we trying to pretend that the commercial is framed in a way that expresses appreciation to men for standing up against violence and bullying and misogyny when its clearly wagging its finger and shaking its head, in a disproving 'tsk, tsk'?