I’ve been in these sorts of situations (had enormous access to critical systems and data and was poorly treated by employer), but logically I just don’t think it is worth the risk to myself, my family, and my future in general to get revenge on these sort of things. It would need to be some sort of Princess Bride situation (“You killed my father, now prepare to die”) kind of thing to bring me to that sort of insanity.

I have also had coworkers that did similar-ish things and they were quite lucky that all that happened was that they were immediately fired and blackballed.