Minecraft wiki entry for Gathering_resources_on_peaceful_difficulty, associated text: Ghast tears, which drop from ghasts, are used to make potions of Regeneration and end crystals. Although both of these are helpful in Minecraft, neither of them could be made even if ghast tears could be obtained in some other way. This is because potions of Regeneration require blaze powder to make, and end crystals require eyes of ender, both of which can't be obtained on Peaceful difficulty because of the lack of blazes.