I think the most important purpose of debate is that it can humanize one's opponents. And this is a very good thing.
For eight years, I moderated a Catholic/interfaith discussion board called Communion. I've had my share of fiery and controversial debates. In my opinion, the most ideal debating situation is not one where people try to convince the other; but rather people attempt to have a conversation, with back and forth, knowing that the other may not be convinced, but in the optic of learning something useful or exercising one's abilities in logic and fact-finding.
I think the posters came to see opponents as human beings because of the culture on that message board. The rules were designed to allow for some occasional manifestation of anger, hostility and rudeness, so that free expression was not too stifled. But, the rules were such that a poster whose purpose was to vent his spleen would either give up because of the "excessive" rules; or he would give up because the posters-- who liked the rules-- wouldn't take the bait; or the poster would get banned.
I have to say that the personality of the posters also helped. They were capable of what they call in French faire abstraction-- the ability to make the words abstract, not personally directed at you.
I can get beyond someone telling me I'm going to hell, or that hold bigoted or racist opinions. And other posters developed the same ability.
And even though one thought another wrong, we managed to develop relationships.
The posters who annoyed me the most were the ones who cut and pasted articles, pulled out the same tired arguments for their side, unable to consider new arguments, unable to consider opponents on an individual basis with personalities and inclinations, and simply treated debate as an excuse to post propaganda and invest nothing else in the process.
Every debater has his own propaganda. Nothing wrong with that. Every one has a their stock responses. What is tedious, though, is the inability of participating in the here-and-now of debate, of examining what is being said, and of treating it as give-and-take rather than a conquest to mow down the other side.
Taking another person's words seriously, responding to them thoughtfully and intelligently, without rancour, has an effect on people who are of the same disposition, even if they disagree with you 100%.
I wouldn't go so far as to say it creates a bond, over the long period, but it certainly predisposes people to be friendlier towards you.
Go to the next section:
On the Purpose of Debate: Part 3
On the Purpose of Debate: Part 1