Didn't the Federation do away with the death penalty in Kirk's time? If I remember correctly, it only existed for travelling to Talos IV, and then only upon sentencing by a court martial. I cannot believe this same Federation would look kindly on the anti-Lex Luthor argument for extrajudicial execution. (It is noteworthy that no one ever tried that on Luthor, either.)
Nor can I believe that Data has been given free reign to abrogate the rights of any other Soong-type androids as some kind of "Soongian emperor." Unless he has been recognized as the sovereign of a state by the Federation, he has no more legal right to commit violence against any other Soong-type android than I do.
I have to agree. The Federation doesn't have the death penalty and, lets face it, being disassembled indefinitely is the same thing as death. Plus we all have to remember that Lore was INCAPACITATED. Data already had him right where he wanted him, and he chose to shut him down rather than arrest him.