Exactly this. People are blaming the pilot, Lion Air, SE Asia, but ultimately a Boeing aircraft decided that it was very important to pitch down and dive into the sea. How many backup sensors and alternate systems have to fail/pass before this course of action is taken? Does the angle of attack sensor not check what a backup sensor is saying, and then what the altimeter is saying, airspeed sensor, and on and on. If a single sensor failing can make this happen then the sensor shouldn't exist.