I just set up "find my iPhone" for a new device. For it to work, you have to go to settings and turn on this feature.
What's to stop a thief from turning this off? Once off, you won't be able to find that iPhone.
Perhaps Apple should include an option of password-protecting that switch. I don't like to password protect from the lock screen, as this is personally inconvenient.
I hope someone from Apple is listening.