I know, that's a pretty bold statement, and in this time of lack of tolerance and constructive debate I can imagine the type of feedback this opinion article will receive.
It's much easier to "sell" why the result of those crashes is lack of trust in the plane, Boeing, the FAA, or software and computers in general, and it is much easier to blame those "deep pocket" entities, but I stand behind this statement. Lack of trust is the root cause of the accidents. Let me explain.
I'm a pilot. That doesn't make me an authority on aviation, but I know enough to make the point I'm making.
Some background first. If you followed the news regarding those crashes and the grounding of this plane, it all comes down to one thing: a software bug. The 737 MAX is equipped with a new software system called MCAS (Maneuvering Characteristics Augmentation System). In simple terms, this system will prevent the plane from stalling (reaching speed too low for flying) by pointing the plane nose downwards, allowing the plane to gain airspeed (which keeps it aloft). The quoted reason for both crashes was that the angle-of-attack sensors fed the MCAS with erroneous data, and the MCAS overrode the pilots handling of the plane and pointed the nose down, automatically. The pilots tried to override the system, unsuccessfully, and MCAS pointed the airplane nose to the ground all the way to the crash location.
So, who's to blame? The first obvious culprit was the manufacturer, Boeing, for not designing the system enough, not testing it enough, or not training the pilots on how to override the MCAS. The second was the FAA for not requiring a full certification of this new variant of the 737. Then, there's software and computers in general that, apparently, cannot be trusted with people's lives.
But if you think about it further, there is another, more fundamental factor. You see, the Boeing 737 took first flight in April 1967, and has been flown ever since. In terms of manufacturing quantities (more than 10,500 737s built), it was second only to the legendary Douglas DC-3 (more than 16,000), but first in number built for passengers. They didn't have MCAS in 737s before the MAX version, yet they flew very successfully.
Did older versions of the 737 not have the ability to stall? Like any airplane, they did. So, how did they recover without MCAS? Simple. They used another type of computer that was available (and trusted) back then. It was the computer installed between the two ears of the pilot. It's called brain. Pilots in control of the airplane used their eyes to see that the plane is losing speed and/or increasing the angle of attack and were trained to push the stick (or control yoke) forward to push the nose downwards to pick up airspeed and prevent (or stop) the stall. They were also experienced enough to know that they sensors are providing false indicators, and wouldn't drive the plane down to the ground intentionally.
But, I guess, at some point we stopped trusting pilots. And the need came for a system that will replace their skills, ability, training, and experience with that of a machine. And that machine made well-calculated mistakes and crashed two 737 MAX planes filled with passengers, killing everyone on board.
No doubt, the failure of the angle-of-attack sensors, the failure of the MCAS software to recognize that the sensors were providing faulty information, the failure of Boeing to test the software enough or provide adequate training on how to override the system, and the failure of the FAA to require re-certification of the MAX variant were all contributing factors. But the main cause of those crashes, in my opinion, is that we stopped trusting pilots.