I know a lot of people who have gone into theater, cinema, and art who left BYU, got caught up in the Hollywood/New York culture, and have completely left the Church. By the same logic we should just get rid of the fine arts programs. Its ridiculous.
What about all of the athletes who went pro and stayed active. Steve Young, Danny Ainge, John Tait...I know there are plenty of others. In truth it can happen in any profession. The best we can do is to prepare them as best we can for the real world and hope they stay true when they get in it.