Let's say FBI has those backdoors they want, how can they make sure that the terrorists won't take advantage of those backdoors? When they can just allow China

Let's say FBI has those backdoors they want, how can they make sure that the terrorists won't take advantage of those backdoors? When they can just allow China to come in and steal U.S government worker's data like http://www.nytimes.com/2015/06/05/us/breach-in-a-federal-computer-system-exposes-personnel-data.html http://www.nytimes.com/2015/06/05/us/breach-in-a-federal-com... I am more worried about them handling the backdoors.