fighter jets are the more extreme and established example, it also applies to most modern airliners which have software systems in place to prevent human controls from exceeding the aircraft flight envelope

fuel efficiency in these modern aircraft has been gained with swept back wings, larger intake engines etc. which with direct control and no software would be almost impossible to keep flying

discarding all of these systems because of a problem with one would set airline safety and efficiency back decades

Swept back wings and larger intake/bypass engines does not make the airframe inherently unstable.

The fly-by-wire system has multiple redundancies and layered protection, including direct law (at least for Airbus). Fly by wire is, like you say, of course a great innovation for improved control and safety, but it's nice when the plane continues flying even during a failure, however unlikely.

I guess in the case of MCAS the software was activity working against the pilots so maybe it's more of a problem with the design of this particular system and training.