Fair point (and bug #6689 for anyone that is interested) but assuming that is the reason for the device unlocking the solution is not to disable the "Switch off" option but to optionally disable the keyboard open magnetic sensor. Being able to accidentally power off a device that has been inadvertently unlocked by a belt clip magnet is just one more reason why bug 6689 should be fixed.

Aside from that, I'm still not sure what is wrong with the secured device "Switch off" option... the only way to get to that state is by unlocking the device screen/keyboard, which is usually hard to do when it is in a magnet-free pocket.