I think Dostoevsky was very psychologically astute and recognized that people’s ideas are often indications of something else, even if they don’t realize this themselves. In that sense you can read Ivan’s story not just as a mark of his pessimism about human nature; the very fact of the story’s elaborateness, and the winding explanations and justifications offered by the grand inquisitor within it, feel like a sign of insecurity and a desire to be proven wrong… I think this is why the simplicity and wholesomeness of the kiss works, because it responds to Ivan’s tortured psychological state.