If Data did what Fajo wanted of him: none, probably.Who is to say how many more people Fajo would have killed if allowed to continue?
Dream on.
That was the purpose of the choice, anyway: "become my possession and I will harm no-one else; don't, and I'll kill again."
The word of someone who had absolutely zero compunction about killing or enslaving any sentient to get what he wanted. Noting also that, once Data was properly secured, he would not be in a position to monitor Fajo's activities or hold him to any promises.
Yep, no problem there.
Killing somebody because they *might* kill somebody else in future is not justifiable. No-one was in immediate danger in this instance.
At least until Fajo got bored and set his sights on some other new toy or amusement. That would happen, certainly.
Do you REALLY think that once he had Data in his collection, Fajo would then never collect (read: steal) anything else, or refrain from killing, harming or enlaving anybody else if it suited him to do so? I don't.