"Dave, I can't let you do that?" You do know that SO allows questions and answers from people without even requiring them to log in? They allow content from essentially anonymous users.

The restrictions are along the "meta" parts (voting to indicate the quality of an answer), I think it is entirely sensible to restrict these actions to users who have built up a currency of trust within the SO community.

That being said, I think you are onto to something around the user experience. Perhaps an option shouldn't be shown to someone if they cannot perform it.