Why Didn't the Death Star Just Destroy Endor

What I don't understand, is if the Death Star were fully functional, and the Emperor was as evil as he seemed to be, they didn't just destroy all of the ships of the Rebel Alliance, and then destroy the planet of Endor.

Some people have suggested it was because it got its energy from Endor. But it seems that they only drew the power for the Death Star's force field from Endor. If that were the case, and they destroyed the rebel fleet, and then destroyed the moon, yes and their energy source, and their own officers, they would have completely crushed the rebel alliance.

Some might say that it was because the rebel ships got close to the Star Destroyers, but I figure the Emperor wouldn't have let a little thing like his own fleet get in the way of killing some rebels.

Ultimately I suppose the Emperor's downfall was arrogance. He left some things to chance and they came back to bite him. Still, I wonder why he didn't just destroy everything to send a message.