Lets forget the argument, that this sets a dangerous precedent for a moment... Even if you assume the strictest possible processes, even if you assume only the most genius techs working on a backdoor like this: In the end the people implementing and operating a backdoor are just people like you and me. People make mistakes no matter how good the skills and processes are. And if this mistake happens, as it will happen invariably, the backdoor is out in the open and usable for adversaries with even more malicious intent.