> A) The bad guys already know, guaranteed

Such a tool would also be useful to prevent* "local hacking" - where your credentials have been hacked by someone in your trust circle. Sad, but it happens. However, luckily for the victims, such people aren't usually aware of the hints they may be leaving after they came.

I agree with your other points.

* Or, rather, retaliate after the deed has been done, but it's a good start.