In this case they help the terrorist and not the government so who do they support? Also no need for a generic backdoor. The FBI can deliver just this phone to Apple secret lab. They do their data magic there and hand over the phone in its original state and the data on a USB stick.
It is more complex than that. Suppose Apple does as you say, and then the FBI's request is found to be unconstitutional. At that point surely Apple would be guilty of a crime.