The FBI is asking Apple to build a tool to backdoor this particular iPhone. Once the tool is built, it gets much easier for them to ask Apple to use it on other

The FBI is asking Apple to build a tool to backdoor this particular iPhone. Once the tool is built, it gets much easier for them to ask Apple to use it on other phones. "We'll only ask for it this one time, honest" isn't a believable promise - Apple winds up with a much less defensible position later, since they already have the tools necessary.