Good reason and judgment. It is the reason that you either elect or appoint judges. We neither desire nor require judges to be simple computers.
And if you think this is arbitrary, then you would equally admit that the justice system in general and the laws themselves are arbitrary. Why you would complain about an arbitrary judge in an arbitrary legal system is beyond me.
That’s a bogus response.
The law is there on the books and I can go to the library and look it up. The judges are bound to apply the law as it is written. Thus, I can make rational, reasoned decisions based on what are rational expectations of the workings of the judicial system.
In your world, however, all of that goes away and we are replaced with a system of “good reason.” One cannot possibly be expected to make rational, reasoned decision when he has no expectation of the consequences whatsoever. It is plain bad policy, and I note that even you are having trouble defending it.