Taking sides is not being closed minded, but a way of seeing a version of the truth. For in taking sides one should have carefully evaluated the situation and come to a conclusion that supports their point of view, or quite possibly change their view.
An essential part of debating involves taking sides. However, if one truly believes their side in the debate is more vigorous, attempting to convince others of your position sharpens the mind so that it becomes a verbal weapon to attack, and hopefully, defeat the opponent.
Taking a side with feet firmly planted in the ground, one can confidently assert their position and show the world the righteousness of their view. By brilliantly putting forth the best argument one can poke holes and show inconsistencies of the other side.
Having a solidified position does not mean dismissing the view of others, but presenting an alternative; perhaps better view. The other side will at least begin to consider that the other side has a valid position: at least mutual respect and understanding will engage.