Why do dogs roll in poop?

So Libby Dog came down the hill today with a big smile on her face.  She was so happy because she had found a big pile of poop to roll in.  Little white dog was half black.  Usually I am sympathetic to her bathing needs and warm up her bath water for her.  Not today.  Today she got the old cold hose and a ton of soap.

Dogs!  Why do they have to be so doggy?  They roll in poop.  They eat poop.  They sniff each others butts, and they love dead things.  And after all that, they want to lick your face.  Acchhhh!