A disagreement usually begins with that's wrong, I don't agree, stop doing that, that's stupid... and then the argument begins. And since one side started from such a strong negative position they have to defend that position, their righteousness and ego is on the line. They are invested in being right. And on the other side the person who is the recipient of this offensive is being challenged, and that challenge may be without any understanding of where they are coming from, for right or wrong, and inevitably they get their back up and dig in. And this is where things get really stupid, fast.
Whereas beginning with a question - Why should we do that? Why do you think this is what we should do? What happens to X if we do that? Are you sure this is the best option for us? - starts with trying to understand the other's perspective and view point. The questioner is open, has no strong statement to make and defend, and the person being questioned appreciates that the other is trying to understand their position.
The questions start a dialogue, an understanding of positions, which typically leads to both parties learning from the other, synthesizing their perspectives into one shared and more than likely, stronger and smarter, position, than where they had both individually stood before.
Start with a question. Learn from the answers. And then express your opinion. Not the other way round.