I don't know what the "official" theory is on how transporters work, but I assume the beam-ee is in effect annihilated at the departure site, and created anew from available matter at the arrival site. This is probably something people have become adjusted to, or prefer not to think about. So naturally, when they beam Christopher back, they figure "It'll be alright" and don't think about it too much.Regarding the transporter solution to get rid of Christopher and the sergeant, I wonder what theory the writer (DC Fontana), director, and producers espoused. I've stated what I think "must have happened," but no one was talking about pattern buffers etc. until the TNG era.