What warrant removes the locks from millions of unrelated doors? That would be a GENERAL warrant, which is something the constitution and this country were created to oppose. This isn't small potatoes. It's supposed to be one of our CORE principles.
I don't agree with you that this is a backdoor into the phone. The data is still encrypted and useless without the complex key that unlocks it. The complex key is still hidden in hardware that would require acid baths and electron microscopes to attempt to read.
The users passcode is the front door that allows access to the complex key. The changes the FBI wants don't provide direct access to the key or the data which is what a backdoor truly is.
I think a better metaphor is Apple has provided, in software, a guard to watch the front door. If someone tries to pick the front door the guard warns them. If they continue he destroys the data.
The FBI wants Apple to fire the guard. The front door is still locked however. If the user used good password hygenie then it can still take years to crack the front door. If he used a four digit pin then it's hours to crack.
While I agree if Apple is forced to make the software than all Apple phones are
less secure. I don't agree that it makes all their phones
insecure. Security of the phone will rest more on the user to create long alphanumeric pass codes instead of relying on Apple to protect weak passwords.
Regardless this is a huge overstep in authority by the government.