One day, Satan woke up and said, "Baseball is pure and good, I must do something about this." He thought long and hard, but could not find a way to introduce evil to baseball. He turned his attention to other things, wars were fought, presidents and princes were killed, history continued on.
Then, one day, a demon in one of the lowest rings of hell came to Satan and said, "Master, I have an idea... a way to introduce evil into baseball." Satan listened to the idea and a smile grew across his face.
"Yes," he said. "Set this plan into motion."
And so the designated hitter was born.
UPDATE: There are rumors that Astroturf was also spawned by Satan... but as it turns out, that was just man being stupid all on his own.