The people at either end have little hope of moving the masses all the way to their end of the argument. Instead, what they do is make it feel safer to change the boundaries, safer to recalibrate the compromise. Over time, as the edges feel more palatable, the masses are more likely to be willing to edge their way closer to one edge or another. Successful zealots don't argue to win. They argue to move the goalposts and to make it appear sane to do so.