The political cost to progressives and liberals for their inability to properly deal with this tactic is greater than they realize. Just as Newt Gingrich was not truly offended by Bill Clinton's behavior (which mirrored his own) neither were conservative congressmen and Rush Limbaugh truly upset by the Move On ad --- and everyone knew it, which was the point. It is a potent demonstration of pure power to force others to insincerely condemn or apologize for something, particularly when the person who is forcing it is also insincerely outraged. For a political party that suffers from a reputation for weakness, it is extremely damaging to be so publicly cowed over and over again. It separates them from their most ardent supporters and makes them appear guilty and unprincipled to the public at large.
I think there's a passage in one of Milan Kundera's books about how the Communist Party would ask grocers to put up signs saying "I Support the Communist Party" (or something) even though both the party and the customers all knew that the sign was insincere. The point, though, wasn't to trick anyone into thinking that the grocer supported the Communists or that the Communists cared whether or not the grocer supported them. The point was just to demonstrate that they could lean on the grocer to put up the sign, and the grocer would do it. Thus, everyone knew that the grocer was a broken man, not least the grocer himself who thus forth would find it that much harder to take himself and his opinions seriously.
These ritual denunciations are like that.
And of course the trap grows tighter each time it happens. The more the precedent piles up that fake Republican outrage should be met by fake Democratic disavowal, the more it becomes the case that it's politically easier to meet fake outrage with a fake disavowal. But at some point, unless Democrats are happy being the Party That Always Loses (and I think there's good reason to think that the consultants who run the party don't really mind) they need to stop doing this and act like people with some self-respect.