Imagine you are walking in the wild and come across what looks like a big rock painted with the following words:
I may look like an ordinary painted rock, but I’m actually a conscious mind. I know about you and your life, and I want to tell you: from the point of view of your values, you should commit suicide. You may have good arguments against your suicide, and I will listen to any arguments you offer, but I know of very good arguments in favor of suicide. I will listen, but if these words have not changed, then my conclusion has not changed.
You may think you are smarter or know more about this topic than a rock, even a rock that can paint words. And I admit that is true of most rocks. But I am not a random rock. I am a honest rock that tries hard not to be overconfident, and that understands how your opinion embodies information that I cannot see directly. I would not say this to most people. I have carefully considered the possibility that you may be right, and yet I remain confident that your best choice is suicide.
This seems to me a clear case of justified disagreement; it is very unlikely that coming across this rock should make you change your opinion on suicide. You have strong reasons to think this is just a painted rock; while the person who painted it probably had a full mind, the rock itself is not listening. Yes, we are biased to dismiss minds that disagree with us so that we can justify our disagreement, but even if we really liked what the rock had to say, we would still think it was just a rock. And so would almost anyone whose opinion your had any respect for.
What variations would make you more persuaded by the rock? What if:
It claimed instead you should not commit suicide?
It claimed instead rocks get itchy and like to be scratched?
It said true private facts about your life?
Skeletons were littered near the rock?
Someone had told you a story of a smart rock?
The words changed in front of your eyes?
It could beat you at chess, or trivia questions?