The problem was never that the plane's flight characteristics were unsafe, it was that they were different enough from the older 737's that it wasn't reasonable to fit them under the same type certificate. So MCAS was added not to make the plane not stall, it was added to make the plane not stall if flown like any other 737.
This is both why a failure of this magnitude could slip past the regulators (MCAS was never described as critical for flight, so it could do with less redundancy. In a failure condition, the crew could always just turn it off and fly without.), and why it's failure is so goddamn galling (a barely-tested computer program that was not needed for safe operation was given the controls to literally fly the plane into the ground for reasons that were best described as marketing).