Being a moderator, people contact me from time to time wondering why their post was deleted. This happens relatively unfrequently, but I think it affects everyone more or less. See, getting your message deleted feels like a slap in the face for most users, and that's not the way it should be.
When you're a moderator, you get to see all of the deleted posts, because they're never really deleted and can be restored. Along with this you get to see the reason for deletion. Problem is, as a regular user can't see the post, they also can't see the reason. (This is also why people like me never give reasons)

My suggestion is simple: let the users see their own deleted posts. This will make them learn from their mistakes (giving moderators a reason to give a reason), stop treating moderators as hostile, and know who to contact if they have questions.