I don't believe that anyone "wins" or "loses" these discussions. But I often come away with a better understanding of the issue - from other perspectives. Sometimes I have my mind changed. But even when an opposing viewpoint doesn't change my mind, it causes me to examine my own beliefs and prejudices more closely, to see if they stand up to the challenges. It can clarify my own thinking to talk it out and have it challenged.
It does matter how the other side is presented, of course. I've never had my mind changed by people just saying "you're wrong you big doodoohead", so it pays to find thoughtful articulate people with viewpoints that oppose my own. There are people here who I don't rountinely agree with that have given me cause to see things differently and have helped me open my mind to some things. But I don't choose to completely immerse myself in opposing viewpoints. A variety of diverse voices is more desirable in my mind. If everybody disagrees with me, or if they're just being strident & offensive, then I feel under attack and it's difficult to hear the valid points made.