My intuition says presenting bad facts or pieces of reasoning is wrong, but withholding good facts or pieces of reasoning is less wrong. I assume most of you agree.

This is a puzzle, because on the face of it, the effect is the same.

Suppose the Walrus and the Carpenter are talking of whether pigs have wings.

Scenario 1: The Carpenter is 80% sure that pigs have wings, but the Walrus wants him to believe that they don't. So the Walrus claims that it's a deep principle of evolution theory that no animal can have wings, and the Carpenter updates to 60%.

Scenario 2: The Carpenter is 60% sure that pigs have wings, and the Walrus wants him to believe that they don't. So the Walrus neglects to mention that he once saw a picture of a winged pig in a book. Learning this would cause the Carpenter to update to 80%, but he doesn't learn this, so he stays at 60%.

In both scenarios, the Walrus chose for the Carpenter's probability to be 60% when he could have chosen for it to be 80%. So what's the difference?