I'm not sure that "fail active" is the alternative.
AFAIK, "Fail passive" means that if a system fails, it won't drastically change anything, but the system will be downgraded.
"Fail operational" means that even if a system fails, the degraded mode will still do what it is supposed to do.
So (something like this) on A320, Cat IIIB is basically "fail operational" - if an autopilot fails at any stage in the approach, the aircraft can still complete an autoland. However, if one is already not working, the system is "fail passive" - another failure will prevent the autoland from being carried out, but it won't leave the aircraft in a mess.
However, the B737 is not "fail passive" below 400'. If the autopilot fails and a go-around is initiated, then the aircraft will be horrendously out of trim, and will require fast work and some dexterity from the pilots to recover it.
Even more particularly, there is a vast difference in an engine failure in the missed approach at 50' on the B737 and the A320.
I am aware of the inadequacies of the answer, but that is a quick attempt to give some idea of the issues at stake.