I have nothing to hide, so I have nothing to fear from any kind of authority that is uncorrupted. However, I must side with Apple on this argument, as all governments are corrupt and data can be leaked through bribes and unsolicited security backdoors, furthermore hackers can use it to do something similar to what happened with the PS3 and the account details that were stolen globally.
So, it isn't as simple as letting the FBI rummage through your data to see if you're a terrorist - that isn't the problem. It's what happens to that data, how it can be stolen and used to create more work for everyone involved. It really is a pandora's iphone.