Why are the stars still on?

Steve at Accelerating Future mentions something that has long troubled me: If intelligent aliens exist why haven't they turned off most of the stars?


Stars waste enormous amounts of useful energy and so speed up the eventual heat death of the universe. You would think that some advanced civilization would have by now sent out self-replicating spacecrafts that would either turn off the stars or capture their energy.

The fact that so many stars still shine means either that we are alone in this part of the universe, or advanced civilizations have access to an unlimited energy source and so don't worry about stars' energy wastage.