Because I think it better, Socrates tells Polus, to be refuted than to refute. Being refuted releases one from false belief, and that is a better thing than freeing someone from false belief. And I count having false beliefs as a very bad thing indeed.
You do another a favor by refuting him. He had beliefs that he hadn’t examined before or not adequately anyway, beliefs that made him, doubtless unbeknownst to himself, quite confused or else exceptionally arrogant. Possibly both. By refuting him, you show him how incompatible his beliefs are, how the one belief in question will need to be gotten rid of or revised, how he would be better off living without that belief (which is false) than were he to continue living with it (knowing now that it is false).
When refuted, one must now hold back from assaying one’s opinion about the subject about which one had hitherto spoken at great length. ‘What do you think: is this painting better than that one?’ I couldn’t say anymore since I don’t know which features make a painting beautiful and excellent. ‘Wasn’t that speech fine?’ I don’t know what fine is, let alone a fine speech, fine linen, or fine dining. In the meantime, might I be better off listening to those who claim to know some things about excellent paintings and fine speeches? Wouldn’t I, from here on out, be more open to considering alternative proposals and novel views? Might I be apt to be inquisitive about other beliefs I have, wondering whether these too might turn out to be false?
Say I thought I knew what virtue was but now I know I don’t. I might make the mistake of giving up on living virtuously, but suppose I don’t. Say I want to live virtuously. Am I not learning that living virtuously means going through each thing I do carefully? It seems so. So, I had better do each thing carefully and speak my words carefully, minding them, minding others? That seems right anyway. Disabused of my false beliefs about virtue, I am thereby already more virtuous. Is this true?