While I think Utah should just let him go, I do understand Whit's point of view. While some say it makes him look small/bitter, I can understand that he probably doesn't want to simply roll over and show future LDS recruits that transferring to BYU after a mission is going to be a cake walk.
In reading Langi's quotes about why he wants to make the move, he never mentions anything that leads me to believe the guy is ultra passionate about returning to the game of football (which is fine btw). It sounds like he is more interested in surrounding himself with like-minded individuals for spiritual reasons.
To me that's a backward way of keeping players at Utah. You don't want to keep players that want to be somewhere else by basically forcing them to stay. You want to motivate players to want to be there and make it a good experience. Trying to force Langi to stay not only is validating his reasons to leave, but setting a bad precedent of negative "motivation"/fear/barbed arrow" type stuff. It shows he's not as interested in the players themselves as a coach should be. If he truly does things to help the players no matter what he will earn respect and players will stay out of a desire to stay and loyalty rather than a fear of exit wounds.
/2cents