As Safetypee said, there is no such thing as safety. There is however a set of design requirements, build since the 1930's by industry and by regulators on the basis of study of accidents and incidents (Car 4b, FAR's and JARs 25 and CS 25) which is continually upgraded with new insights by working groups and panels. The MCAS problems and resulting events are part of this proces and will eventually find their way in the regulations. IMHO the regulations are the pinnacle of human knowledge (so to speak) but the real effort is in the compliance finding to these regulations, by the regulator and airworth8iness authority.