Why are slaves always revolting?

A friend of mine (thanks Tom) suggested introducing some poor quality troop types to the game to contrast with the elite forces of Rome. So i managed to find some good slave figures from 1st Corps Miniatures and put together a warband of freed slaves. These slaves have been promised their freedom in return for service on the field, they will add real character to a game but I don't fancy their chances much against the mincing machine of Rome. I'm Sparticus!...oh no wait...there he is.