Gramps once told me about all the empires that fell over eunuchs. The problem was that they thought cutting the nuts off someone made them more controlable or less a threat. It really made them very vindictive and evil. He told me never to make a eunuch of a slave if I had any use for him whatever. They shouldnt be councellors, harem guards, administrators or toilet cleaners.
He did however tell me that if I did ever decide to make a eunuch of someone for a penal reason, to keep them locked up somewhere and dont use them for anything.
When people pried into my head about this they missed this last part and thought no matter how mad I got I would never order anyone to be made a eunuch. Too bad for them on that.