This isn't a decathlon. I don't want to watch Jonathan Quick play center, Lionel Messi play goalkeeper, or Peyton Manning play safety. I don't want to watch Albert Pujols pitch or watch Jered Weaver bat.
I don't want to watch the worst hitters on the bench come up because you have to hit for the pitcher. If a pitcher is throwing well, but the bases are loaded, I don't want him to be taken out because he can't hit. The DH makes baseball a better game and more appealing to the masses. That's why everyone uses it except for the National League.