(a) some random drop of the dice already sealed their fate. If anything, being admitted to an experimental group and then clustered into control or not, is the DM giving a second roll of the dice.
(b) most therapies don't improve prognosis in terminal cases and some make it worse. We don't know which beforehand. In the cases where the therapy makes it worse, was it therefore immoral to not put more people in the control group?
I'd argue the lack of knowledge makes it a wash morally. If we knew beforehand whether the therapy would be effective, we wouldn't need the control group, but we also wouldn't need the study.
(b) most therapies don't improve prognosis in terminal cases and some make it worse. We don't know which beforehand. In the cases where the therapy makes it worse, was it therefore immoral to not put more people in the control group?
I'd argue the lack of knowledge makes it a wash morally. If we knew beforehand whether the therapy would be effective, we wouldn't need the control group, but we also wouldn't need the study.