That difference is also a benefit, fix one problem, and it's fixed for every instance.
On the other hand, it's not like the software is always bad and always in the same situation. That is a big difference with a human analogy; a drunk driver taking a trip in the car is drunk for the entire trip (unless it's a very long trip etc..), so would be impaired for the entire duration.
There are plenty of people and vehicles that are road hazards and are allowed to drive (or be driven) anyway, so if we really cared about that aspect on its own we could probably do with better tests and rules in general.
On the other hand, it's not like the software is always bad and always in the same situation. That is a big difference with a human analogy; a drunk driver taking a trip in the car is drunk for the entire trip (unless it's a very long trip etc..), so would be impaired for the entire duration.
There are plenty of people and vehicles that are road hazards and are allowed to drive (or be driven) anyway, so if we really cared about that aspect on its own we could probably do with better tests and rules in general.