Depending on details, it may not be an unreasonable request. The question is more one of trust: do we trust the FBI that it's a reasonable request?
This is why all the stuff like the activities the Snowden leaks demonstrated or Trump's idiotic harassment of the press through the DOJ are so harmful far beyond the direct harm they did: they justifiable and seriously erode trust, and then there is a serious case like this and "trust us" no longer carries any value. A sad state of affairs where everyone loses.