The reason for an MEL and things like ETOPS, in the FARs is because without them safety would only be in the eyes of the beholder. It provides a minimum level of protection/safety for the general population.

MELs came about after accidents ... Basically bargained for by operators.

ETOPs came about after a close call where an L1011 (I believe) touched down after losing 2 of the 3 engines ... And the 3rd engine was on the way ... All three had an oil seal installed incorrectly.

No safety forethought involved in either MELs or ETOPs ... Both were reactive.