Re: So what is going on?
It's also desirable to be able to disable the transponder in the event that it malfunctions - you don't want it broadcasting false information to ATC, or worse yet, you don't want it setting itself on fire.
There seems to be a lot of people focusing on why transponders can be turned off, but what benefit would keeping them on at all times actually provide? They are a radio transmitter, which would be next to useless over the oceans anyway, so even if it had been left on, we'd still probably be non the wiser as to the planes location until it made landfall somewhere (assuming it managed to do so).