I am one of the seemingly few airline pilots who wouldn't mind cameras in the flight deck, as long as they were properly used (ie NEVER by the management and only for accident investigation or viewing by the CREW THEMSELVES for personal debriefing).
I think cameras in the cabin to look for incapacitation are a waste of money. The cabin crew can call and if unanswered can apply the "other procedures".
You have to look a bit further beyond the cameras too. What happens if say both pilots have passed out due to lack of oxygen - what would the cabin crew actually do to remedy the situation?
A number of the things reported by the media about the Helios accident have since been discredited (the text message especially) and I think there is a lot of supposition around. The likelihood that cabin crew were conscious and the flight crew not, in what little I know of the situation looks unlikely. It is also such a low possibility that both pilots will be unconscious and the rest of the aircraft OK. Sleep is a different matter and is easily remedied by current procedures.
Secondly, what happens if the system is unservicable? Can you still fly, and if so, how long before it needs to be repaired? What about passengers, could they see it too? If so, they could easily overpower the cabin crew and look and wait until one of us was ready to use the loo.
Also, why spend zillions on a camera, when a spy hole would do? No need to worry about whether the camera records or not. If it is just a device to see whether the pilots are still alive or not, then why make it complicated? To go super high tech, it could be fitted with a wire locked cover and used for emergencies only.
I wouldn't like to see a screen where we could be watched. Many crew don't suitably understand what we actually do, and I would be loathe to be critiscised by what someone saw on the "telly".