Turning Off Transponders -- Aviation Security and MH370

In an earlier post regarding MH370, I wondered why it was that transponders on airplanes were still capable of being turned off.  I feel rather justified to realize that I’m not the only one asking the question.  Gregg Easterbrook has an op-ed in The New York Times in which he makes the same point and amplifies it with the point that 5 of the last 10 major air disasters began with the transponder being switched off. But that, it seems, is not the whole story.  John Villasenor, a Brookings Fellow and an Professor of Electrical Engineering and Public Policy at UCLA writes in with the following thoughts that trend in the opposite direction:

With the caveat that I am not a pilot, my understanding is that the ability to turn things off in flight is due in part to historical aviation "lessons learned" from onboard fires. Obviously, a fire onboard an in-flight airplane is very bad news, and to the extent that electrical systems have often been the source of such fires, planes are often designed so that pilots can take action to shut off electricity flow to various on-board systems. Now, it's certainly possible to do a risk-based analysis to assess, in this day and age, whether it still makes sense to have the transponder circuit breaker accessible from the cockpit. Even if someone were to conclude that pilot access should be removed (and I am not saying I back that conclusion, just that, it is a possible conclusion someone could make), there would be both mechanical and cultural obstacles to actually implementing that change in the thousands of aircraft in commercial service today. I've also heard of (extremely rare) cases where transponders malfunctioned in flight and started transmitting the *wrong* altitude. Obviously, that's worse than no transponder at all. When that happens, the pilot can turn off the transponder and then contact ATC with altitude info - cumbersome, but much better than allowing the malfunctioning transponder to continue to send incorrect info to ATC.

And that, at least, is a partial explanation.