Let’s assume that Apple does help the government subvert the security of iPhones by getting them into this one device. This is not Apple’s specialty. I wouldn’t hire a safe builder to crack into a safe. I’d hire a safe cracker, but that’s just more about how the government is being disingenuous when it says this is about just one phone.
Anyway – once the government has access then we live in a world where all iPhones can be opened. At first it will take a court order to get access to a phone. Then the code will leak out, and it will leak out. Consider who has been compromised in the past. Places like Sony, OPM, IRS, and even the Pentagon. Once there’s a program that is a back door to all iPhones, it will be stolen. Once that happens all iPhones can be opened. Will Joe Criminal continue to use iPhones? Of course not! Criminals will do a google search (Yes. Criminals have heard of the Internet.), and they will use some other technology to keep their communications secret.
Let’s say that the politicians get involved. They talk about how this encryption stuff is obviously dangerous, and it must be regulated. Remember, we did this before. Let’s say that they require all products sold in the U.S. to have back-doors built in so that law enforcement can have access to all encrypted secrets. They’ll say that it’s only law enforcement, but later it will be any well funded group like China, ISIS, or perhaps a political party looking for dirt on people. What will happen next? The same thing that happened when the U.S. government declared encryption to be a munition and regulated it. All people and organizations that value privacy will use encryption that’s not broken. They’ll get it from outside the U.S. But wait! You say congress is smarter than that. They will make it illegal to use such encryption. Once that happens, all people who obey the law will use broken encryption. All people who value privacy and who are criminals (terrorists, drug dealers, etc.) will use encryption that works.
Breaking the encryption never hurts criminals over the long run. It always hurts good, law-abiding people.
When terrorists in Mumbai used cell phones there was talk about how cell phones can be dangerous. Yet we understand that the devices do far more good than bad. Privacy likewise does far more good than bad. Without privacy we are open the whims of those in power. If the government has access to the private communications of all citizens then what happens when our next President decides to use an executive order to punish those who pollute, or those who own firearms, or those who speak ill of another religion. Privacy protects us all. If we sacrifice privacy in the name of security then we’ve lost both.