When has it ever happened that someone changed their opinion in an argument? But I still respect all the opinions presented. I have a good friend who is a devout Orthodox Christian. And I have complete mutual understanding with him, because we simply don't try to change each other.

An argument is a "test" of an opinion's strength. In an argument with others, we can notice problems and contradictions related to our opinion that we didn't see ourselves, and correct and supplement our position.