If you honestly believe the FBI hasn't already accessed that device, you're as naive as anyone else wanting them to unlock the device. It's not about just this device, it's about the FBI having an easy backdoor access to virtually any device they see fit, with or without a warrant.Dont get me wrong, Im all FOR privacy, but NOT when it comes down to the lives of others. If the information on that phone had the potential to save thousands of lives, then YES, it should be unlocked, of course! If you believe that the information on that phone should stay lost forever, then theres a high chance that another terrorist attack or other serious crime could have been prevented, but you DIDNT want it stopped (even though you knew there was a chance you could have stopped it).
Why would you want to toss away innocent lives because you believed TOO strongly in privacy to take it to extraordinary extremes? Thats just dumb thinking. Privacy should be enforced, I have no objection to that, but there comes a point where that has to be overridden for the bigger benefit. Dont be selfish and try to make ALL information private permanently. In this case, yes, the information SHOULD be unlocked so that future potential criminal activity has the possibility to be prevented. Something is more than nothing.
Please, do more research. There is so much that I feel like you haven't read, or aren't willing to read.