That is: what’s an example of an argument for which the motives for assuming it are actively pleasant? What follows from their pleasantness?
A policy like “assume good faith” strikes me as coming from not unpleasant motives. What follows is that you should attribute a higher probability of good faith to someone who assumes good faith. If someone assumes that other people cannot be convinced by evidence, my knowledge of projection suggests that should increase my probability estimate that they cannot be convinced by evidence.
That doesn’t entirely answer your question- since I talked about policies and you’re talking about motives- but it should suggest an answer. Policies and statements represent a distribution of sets of possible motives, and so while the motives themselves unambiguously tell you how to respond the policies just suggest good guesses. But, in general, pleasantness begets pleasantness and unpleasantness begets unpleasantness.
A policy like “assume good faith” strikes me as coming from not unpleasant motives. What follows is that you should attribute a higher probability of good faith to someone who assumes good faith. If someone assumes that other people cannot be convinced by evidence, my knowledge of projection suggests that should increase my probability estimate that they cannot be convinced by evidence.
That doesn’t entirely answer your question- since I talked about policies and you’re talking about motives- but it should suggest an answer. Policies and statements represent a distribution of sets of possible motives, and so while the motives themselves unambiguously tell you how to respond the policies just suggest good guesses. But, in general, pleasantness begets pleasantness and unpleasantness begets unpleasantness.