This is a very good point - as long as your goal is really and only to have the opinion that is closest to the truth, and you're completely open to changing it when new evidence comes. In other words, if you are really discussing because of the right reasons (which should of course always be the case).

But in many contexts, this is not the end goal. The end goal is to either make one feel better about its own beliefs, or to exert social pressure/gain social status.

You can often kind of tell who is really discussing to find the underlying truth based on this very observation.