The ones who choose to stay willingly are. Unfortunately not every Amish child is given the same opportunity to choose for themselves and that's a problem. They are getting better about allowing outsiders to join their lifestyle, but it still needs improvement. If they laid out a list of simple rules to follow that didn't require a spiritual commitment, their numbers would likely increase healthily over time while their children choosing to stay or go wouldn't have as much of an impact on their culture.