Employee: Vernonʼs behavior in last monthʼs incident was certainly unprofessional enough that our company was justified in firing him.
Conclusion
If the company is going to be consistent, then they must give Vernon his job back.
Evidence
Vernon got (rightfully) fired for unprofessional behavior, but several higher-ranking employees who acted similarly didn't get fired and are even in good standing.
Evaluate
We might intuitively be offended by this argument and hear ourselves saying,
If that didn't occur to us, we would try to get there by attacking the conclusion.
We would need to argue that
At that point we might think, "the other way to be consistent would be to fire the other people who should have gotten the same treatment as Vernon.
Goal
The answer will almost certainly be expressing our sentiment that you don't need to re-hire Vernon to be consistent, you could (and probably should) choose instead to just fire the higher-ranking employees that so far have not been punished.