I'm often told something that I disagree sharply with and argue against forcefully. And then, 6 weeks later, I am putting forward the new idea, the one I hated, to someone else. And somehow, during those 6 weeks, my resistance melts away and I become the one promoting the idea. This has happened to me, literally, 100s of times. I'm given a new idea which I hate so I fight against it. Later I accept it. I've noticed this sometimes happens to my friends too.
I would say it's rare for debate to change anyone's mind, but that it does happens sometimes. In any debate there is the 45% hard core on one side and the 45% hardcore for the other side and the 10% in the middle who can still be influenced. And all debate is basically aimed at that 10% in the middle.