MCAS did not fail. The AoA subsystem did, producing erroneous data and a false stall warning. MCAS did exactly what it was supposed to do based on the information it was provided. Isn't the suggestion for pilots to push the nose down when there is a stall warning and stick shaker? While MCAS wasn't designed to detect or react to stalls, and appears to have no such input, it is supposed to provide a correction to a high AoA and it did. The FAA, Boeing, foreign CAAs, and all pilots trained on the 737 NG already accepted the chance for a false stall warning and had done so for, estimating, 2 decades.