Why prove to a man he is wrong? Is that going to make him like you? Why not let him save face? He didn't ask for your opinion. He didn't want it. Why argue with him? You can't win an argument, because if you lose, you lose it; and if you win it, you lose it. Why? You will feel fine. But what about him? You have made him feel inferior, you hurt his pride, insult his intelligence, his judgment, and his self-respect, and he'll resent your triumph. That will make him strike back, but it will never make him want to change his mind. A man convinced against his will is of the same opinion still.
When a subject is highly controversial... one cannot hope to tell the truth. One can only show how one came to hold whatever opinion one does hold. One can only give one's audience the chance of drawing their own conclusions as they observe the limitations, the prejudices, the idiosyncrasies of the speaker.