So it happened, the US government is trying to compel Apple into creating a backdoor into iOS. This is a dangerous precedent. Sure they'll pass it off as an 'issue of national security' but it's just not that simple.
iOS is designed to be secure. This means there is no way for even Apple to access the encrypted data on the device. This is a practice we call 'secure by design'. Apple has done their best to ensure there is no way into the data on the device.
The US government asked for an IPSW file to access the phone. This file would contain a security hole that would give them access to a phone. The mere existence of such a piece of software makes iOS no longer secure by design.
What would stop this software from falling into the wrong hands? Do you honestly think such a tool would not be used in spycraft? After all that has come to light on warrantless spying using 'Stingray devices' do you even trust them with such a tool?