Originally Posted by
EyeKantEven
Well said. That's exactly it. That's called "negative longitudinal stability", and it's a deal-breaker for certification.
The electronic workaround (MCAS) was clever but poorly executed, starting with the single point of failure, pilot-side-only AOA source, and ending with the "invisible system" that pilots had no idea.
MCAS was a subsystem, a subsystems of the Speed Trim System. The STS has several other modes besides MCAS. They all fed off one AOA because that is all that was required. The STS was not considered a safety critical system and malfunctions were not rated greater than hazardous.