It's like everything we do in life, it's all about risk, calculated risk.
The complexity of modern Airliners is getting more in some ways yet less in dealing with it. Black cockpit, redundancy's less is more etc all make for a low workload when normal Ops & moderate yet acceptable work load when non NO Ops. Look at QF32, had that happened in the future with one driver at the helm then that could very well have been the end.
Also it's like why have multi-engined planes? I mean the power output of the biggest engine today is well over 100000lbs thrust, more than enough to propel 250 sets thru the air but we don't allow it, too risky too dangerous just like SP Ops in modern day Airliners.
Where does the future lie?............pilot-less A/C, it'll happen am sure but not in our time:-)
Wmk2