All sports are art-forms, and are subject to imperfection. That vulnerability gives art its sense of danger and its humanity. Baseball would lose much of its suspense if a wrong call were never possible.
The beauty of baseball is in its details as metaphor: you never know when it will end; it's extremely difficult to do well; when done well, it's beautiful; our differences are best resolved from a distance; excellence is often not rewarded.
The metaphor also applies to the way the game is umpired. We don't watch the game "because we value the idea that the umpire might screw up." We watch the game becomes it remains beautiful—complex—even when the umpires do screw up. Painful, frustrating, yes—but human, graceful, and worthy of our time.
If you don't believe me, look again at Armando Galarraga's smile when Joyce got the call wrong. Consider Joyce's tears acknowledging his error. Life, like art, is that way sometimes—a record of missed opportunities. What can you do?