It's not about the disagreement but the facts surrounding the argument that determines if someone is viewing things objectively or has made up their mind before hearing a particular point of view.
I have observed the good leaders are able to sometimes change their thinking based upon a valid argument and of course, there are others who think that they already know the answer, so why have the discussion? It is hard to fill a cup which is already full. Yes, I got this from Avatar. And yes, I'm well aware that it was said before the movie.
So how do you change that thinking? The thinking in which someone knows the answer before the question is asked or discussed? Well, I don't have the answer because I'm still learning. Maybe trial and error is the key. To let one try it out and figure it out for themselves. It's the hardest way to learn, but at least you learn.