Why Does Santa Give Naughty People Coal?

Everyone knows that if you're naughty then Santa will bring you a lump of coal for Christmas. Since the beginning of Christmas, serial killers and assholes all over the world have awoken to a big lump of coal in their stocking. I've always wondered why Santa chose coal, especially since it's a useful item for some people.

What if you've been really naughty and happen to have a coal powered generator in your house? Do you still get coal or would Santa give you something you can't use like reindeer cum? Where does Santa get his coal? Is there a lot of coal at the North Pole? It probably would be easier for him to just procure reindeer semen, but then again that might tire the reindeer out, so I can see why he doesn't do that. I think if I were Santa instead of giving coal to naughty people I would just dump pour the glass of milk they left for me on top of their heads while they're sleeping. Then they have to spend their Christmas day washing their sheets so they don't end up smelling like spoiled dairy. Doing laundry on Christmas is WAY worse than coal. Think about it Santa, think about it!