Aerobatic, crop spraying and fighter aircraft have to be unstable to allow for rapid maneuverability. A crop sprayer pilot described flying the Ayers Turbo Thrush to me as "like balancing on a beach ball".
Some of the latest fighters are so unstable that they have to be fly by wire or control would be rapidly lost by most pilots.
The certification requirement of not needing undue "skill, alertness or strength" needs to be remembered. IF the MCAS has to be watched like a hawk and requires a couple of night club bouncers to overcome a simple failure then it has no place on a civil aircraft. Imagine two slightly built female pilots trying to overcome a runaway system.