Case 2: Agreed, but not everyone is lucky enough to work for a competent manager. And managers don't fit neatly within competent and incompetent buckets. Under external or higher pressure ("his job or your job") a normally decent manager might make that call.
Case 3a: Good distinction, a conscious leak is not a mistake. It's possible for a leak to be accidental though, say under alcohol, lost laptop, or just caught off guard by a clever inquisitor.
Case 3b: Firing has the effects you mention, but it also has the effect of assigning gravity to that error. I'm not claiming the benefits outweigh the drawbacks, but some managers do.
I'm not a proponent of the above, but it's good to understand the possible rationale behind these decisions.
Firing someone over making a mistake is never a good idea.
If you're going to have firing offenses, spell those out. E.g. breaking the law, violating some set of rules in the handbook, whatever., so that people can at least know there's a process or sensibility to the actions.
If people can be fired for making a mistake, and that wasn't laid out at the outset, then they're just not gonna trust the stability of your workplace.
Case 3a: Good distinction, a conscious leak is not a mistake. It's possible for a leak to be accidental though, say under alcohol, lost laptop, or just caught off guard by a clever inquisitor.
Case 3b: Firing has the effects you mention, but it also has the effect of assigning gravity to that error. I'm not claiming the benefits outweigh the drawbacks, but some managers do.
I'm not a proponent of the above, but it's good to understand the possible rationale behind these decisions.