Corresponding to my previous post of Dark Water/Death in Heaven, what is the worst thing do you think the Master/Missy has done over the years?
Personally, I would think uploading dead souls into Gallifreyan hard drive, and converting them to Cybermen from the Cyberspace would be the worst. Because it perverts the sanctity of death itself, which is even worse than killing. There should be honor in life and death, both.
Your vote: Keeping his own kind in a suspended state on the brink of death, to make them into CyberMasters